Common amateur mistake

Tension is often a good thing, by keeping tension in the centre you make your opponent think about all the different possibilities where White takes on d5, every move. By pushing c4-c5 as you rightly said, Black can now play for e5 in safety, since d5 is no longer in any danger. And also, as you said again, b6 is now an option for Black. I think you're pretty much spot on actually! I play similar positions with the f pawn on f5 (Stonewall Dutch) a bit, and after c5 I always follow up with the e5 plan which gives Black a good game quite often.

Of course, if White can follow up such a move with quick action on the queenside, it may be correct - it all depends on position. But a lot of the time ,and certainly in this position, it isn't very challenging for Black.

Thanks, I knew from experience that this is a bad move, but wanted to be able to better articulate exactly why. 

I think you make a good point that while it offers white some queenside play, black will be able to neutralize this fairly easily.  Meanwhile, white has given black a clear plan of central expansion.

Black can play ...b6, ...a5, ...Nbd7 which undermine White's pawn center. That's why move c4-c5 makes alot of counterplays by black and a target within the game.

I didn't like the move because of the plans of Black given by -waller-.

I prefer to stay my pawn on c4.

@pellik, I think c5 is only a viable plan if white is able to conjure up a queenside attack before black is able to break in the center and launch a kingside attack after the e5-e4 push.  The locked center calls for quick attacks on the opposite wings.

Controlling the e5 square stalls blacks counterattacking possibilities.

One very generalized way of looking at these types of moves is this:

Before you push c5, the c pawn has more options (and therefore so do you). One of the options is c5, of course, but as soon as you make it, the pawn has no more options. 

By contrast, a pawn on c4 might one day find it advantageous to capture on d5 (or even b5). Or it may some day support a piece on one of these squares. So why not leave your options open? Play c5 if you have an immediate need for c5 and can articulate your reasons to yourself. In the above position, it was certainly not more important than continuing development. Worse than that, it makes it much harder to challenge the central pawn on d5.

A lot of times back when I was younger (around 1400~ strength) I would play something like this with both white in a 1. d4 line and as black in the french advance. It works very well against players around 1400 strength and lower as you can squeeze them to death, and I have many a won game from it. It doesn't work so well against players above that indicated strength. 

My reasoning for playing this way is that it can hinder the opponent's natural development. Played right, and you can get an open b-file on which to base your play on and a very nice outpost on b3 for a knight. I'm less inclined to play that way now (although I did play a game OTB a month ago in this fashion, leading to a 14 move draw because I overextended myself) and more inclined to go after weaknesses. But it is an easy, solid plan for players just starting out and can help themselves wrap their minds around the concept of making a plan and following it.