1.d4 e6!? ... have you ever seen this variation?

I wouldn't even worry too much about be7, or nf6, regarding exchange variation. At higher levels black is showing ways of playing the Nf6 lines, and lower ones, I don't know sub uscf 1500, have no clue how to exploit minority attacks and other subties of exchange variation. 

many times and can transpose to most variations

Short used to like 1. d4 e6 as black, because he liked the French and the Dutch defenses. And he was a world class player, so his preference deserves to be treated with respect.

^ or the Modern Benoni

The english defence 1.d4 e6 c4 b6, and Keres 1.d4 e6 2c4 Bb4ch are two reasonable openings can only get with the 1.d4 e6 move order.

There is a book "1.d4 Beat the Guerillas" by a IM, which tries to suggest strong, sensible replies against unusual 1.d4 respones. He has quite a lot of trouble with both the above. The English defence might be borderline refuted but the best line gets quite crazy, so still potental problems OTB for white. Whilst, the Keres has some very solid lines. 

The English Defense doesn't look very logical to me. What's the crazy line and why is it best for white?

Yes, Korchnoi was relying on it not looking very logical when beating Polugavsky with it in candidates match in the 70's. 

1d4 e6 2c4 b6 3e4 bb7 4bd3 f5 5exf5 then both 5 ...Bxg2 6Qh5ch , and 5...Bb4ch 6Kf1 get quite messy, and normally not what the solid d4 player wants. Objectively the positions white reaches with best moves might be very good for him.

Something like 3a3 might keep couterplay like bb4 undercontrol, but objectively black might be able to reach equality.

There are lines like 1.d4 e6 c4 Bb4ch 3Nc3 b6 where black avoids the "best" line, and still has english defence ideas of f5 undermining white's centre.

Space in chess is considered an advantage. So a coach is going to want to teach you lines that allow you a fair share of space.

1.e4 e5

or

1.d4 d5

These usually are the Classic way of playing chess.

The Queens Gambit Declined which is 1.d4 d5 2.c4 e6 will never be considered terrible. It is classical chess and it will never be refuted. I do believe;however, their are some lines that are not played so often in high level any more. I rememeber Kasparov giving up against Karpov the Isolated Queen Pawn line. I can't rememeber the name of it. I think its called Tarrasch or Tartakower;however, I honestly don't play it as black so I don't know which line it is.

Also if you find yourself not liking the Queens Gambit Declined. It might be due to your playing style and not the line you are playing. Unless you are playing a terrible verison of the QGD. However, if the line you are playing is considered reasonable than it might be your playing style that just does not like the position's. Not every chess player in history played the QGD because it was just not in their style.

Considering you are learning chess from a coach maybe you should consider asking about the below move order

1.d4 d5 2.c4 c6

Its the Slav Defence

Its another way of playing Classically while getting fair share of the center. If you find yourself not liking those positions either well than. Maybe you should face the fact lol that you have another Daddy(Father).

What I mean by that is William Steinitz is considered to be the Father of Classical chess.

Answering a center pawn with a center pawn.

1.e4 e5

or

1.d4 d5

If your opponent doesn't play a center pawn than you play a center pawn

1.c4  e5

1.f4  d5

1.Nf3 d5

Classical Chess at its finest. Show by William Steinitz

If you do not like those position's it means you are the Baster Son of Aron Nimzowitsch. So you have another Father Luke lol. Your a Hyper-Modern Player.

How wonderful I have a new brother or sister. Welcome to the family.

The problem with 1 ..e6 is that it give white a large range of additional options and extra opening theory that Black will need to be knowledgable of.

2. e4 is played about 75% of the time and the result is almost always a french, which I assume black is comfortable with. I do know that white making this 2. e4 choice should be comfortable playing against the French. Other than that Black could try the rare 2 ..b6 which I don't think is good as white has lots of space. Or try an equally rare 2 ..c5 which could transpose into a Sicilian but with e6 played early, or going into a broad range of other openings also with an early e6.

The other normal move is 2. c4, which does have more options. If black intended to meet 2. c4 with Nf6 or d5, that doesn't make much sense to me as why not just play d5 or Nf6 on turn 1 and anchor your opening paths? 2. c4 f5 same idea why not just play 1. d4 f5 instead? Thing is It is not tricking white at all as white almost always plays 2. c4 anyway.

In summary I think the intent for black's 1.d4 e6 is to either get into a French defense or an English defense (English and French... interesting), which I suppose makes sense as they are both of the counter attacking type of defense. As mentioned if the intent is to meet 2. c4 with stuff like Nf6, d5, f5 they all should be played on turn 1 instead as I don't see any benefit of "inducing" 2. c4. Black is usually okay with at least one of Nf6, d5, or f5 to begin with against 1.d4 so 1 ..e6 would not be useful.

Have to say when  I play  1d4 e6 whether white thinks the move makes sense or not isn't a high priority.

@wrathss Obviously you were looking at the chess.com database and not at anything more useful- chess.com's database doesn't work as it should- it does show all transpositions, but if you are transposing into a more common variation, it makes it look like that move is more common. Obviously, there's no way 2. e4 is played 75% of the time after 1. d4 e6. People who start with 1. d4 are intending to play Queen's Pawn openings, and if you see any random d4 player facing 1...e6, odds are much higher that they will play 2. c4 or 2. Nf3. For evidence of this, go to the much better 365chess database, which will show you that 2. c4 is about five times as common as 2. e4, and 2. Nf3 is also twice as common.

If you do play the French, the move order makes sense. If you want to play the Dutch, you avoid the Staunton Gambit and 2. Bg5. If you want to play the Nimzo or Benoni or something, you avoid the Trompowsky.

I would say that if you do play the French defense and you want to play a Nimzo or Q.G.D. or even Dutch as black against QP openings, 1...e6 makes a lot of sense.

my dad loves to play it

Some may disagree, but frankly, I think the biggest disadvantage of 1. d4 e6 is that your opponent can play 2. e4 (which he mostly won't do). The Nimzo is theoretically black's best reply to 1. d4 and this move order avoids the Bg5 lines and allows black to transpose into it, and other related lines like the Bogo or Q.I.D. I don't think most GMs would say the French is the best reply to 1. e4 (probably the Berlin, given that black's theoretical goal is a draw). But it makes no difference. Super-GMs can't really refute the French, and they certainly can't refute the move order. I might even use this move order sometime soon- I play the French from time to time.

It's only the most played opening in world championship matches...

You would think someone playing 1.d4 e6 would be playing something consistent with what played after 1.e4, after 2e4, probably the french. Serious clubplayers would try to build a reliable rep. In the french, there are many less popular lines, which still can be played in usual french fashion. For example  have tried 1.d4 e6 2e4 d5 3Nc3 Bb4 4e5 Qd7. Would expect the typical 1.d4 club player not to be so familar or practised in this line. Who knows though, maybe a recent convert from 1.e4 player?! That's what opening play is all about thought isn't? Trying to trick opponent into something less familar than you are. You don't really know if worked till postmortem of game. Some players keep their secrets even then.

@dpnorman well I got 75% from the chesstempo.com database, which by default only has games of players rated 2200 or higher (2200+ vs 2200+). I changed the filter to "all games", "2700+ vs 2700+" and other possibilities and 2. e4 remains at 70%+. A general pattern is that the higher rated the game the more rare a French occurs.

Fundamentally it is hard to deny that the overwhelming options against 1. d4 is either 1. Nf6 or 1. d5, both of which does exactly stop e4 and precisely why they are good moves and other moves are rare. The problem with d4 e6 again is white is not tricked at all. If white likes the French 2. e4 will be played. If white likes d4 openings white will play 2. c4. Either way the choice is white's.

The only possible explanation is that black is a French specialist (a rather rare bird I have to say. I used to play the french at times but I never imagined playing it against 1. e4 100% of the time), and playing 1. d4 e6 black will have a lot more French defense games. I guess it depend's on how well black plays the French and whether the score is better than normal d4 replies.

Personally in this situation I play 2. e4 100% without question because from white's perspective this is like playing an e4 opening at the same time avoiding the Sicilian and Ruy Lopez. If there is a rule that if white plays 1. e4, black is not allowed to respond with 1. e5 or 1. c5 and can only play the French, I would switch to e4 in a heartbeat as I have a very good score playing the Tarrasch and I totally welcome this transposition.

I have found that a lot of Austrians play the move 1.d4 e6  hoping to play the Kangaroo Defence

Those funny aussies.

Sorry but nonsense. 2. e4 doesn't count as being an addition to white's "wide range of choices" because he could have played that on the very first move if he wanted to, this is assuming black would play 1. ..e6 to 1. e4. It doesn't give ANY extra choices to play it on the second move.

It's logically hypocritical to play the French and not play 2. ...e6..... and yet to play 1. e4 yourself. Think about it: the only way it would make sense would be if black were to consider 1. d4 with that whole QG complex to be a significantly superior move to 1. e4. It's not often you can work something out logically like that in chess but you can with this.  

If white plays 1. e4 black can play 1. e5 or 1. c5. However, after 1. d4 e6 now 2. e4 is completely different logically because white now knows black cannot play a Sicilian or a Ruy, but will be playing the French. Again if I play 1. e4 and know I can avoid Sicilian or Ruy and it will be a French I am sure a lot of players will switch back to 1.e4.

"Logically", again:

1. d4 Nf6. White goes down any of the QG lines

1. d4 e6. White goes down any of the OG lines, or go into a French.

Which is better for white?