Why a4?

Simple and makes sense.  Thank you

You activate your a1 rook and try to prove that the b5 pawn is a weakness

Puzzling. You have a diamond membership, but you hate v3....

Fascinating.

Couple things, first with a rating of 1077, you can't worry about the positional (non-tactical) stuff that the computer calls "inaccuracies".  Most of it is too subtle for that rating level.  You want to worry about stuff that it labels a blunder, and I believe "mistake" is the intermediate level between inaccuracy and blunder -- you can learn from some of those too.  Second, you need a plan to develop every single piece on the queenside as you are all blocked up.  Third, e5 actually looks totally fine to me -- while it doesn't address you jammed queenside, it is a bit awkward for black to deal with and saying the position is only +.22 in white's favor it a bit stingy (although again, that queenside is awkward too).  (Edit:  confirmed with stockfish, E4 is a good move, just not as good as a4).  For the record, a4 isn't just about weakening black's pawns -- it is actually a very subtle way of improving your queenside, since the idea is that the next move the queen probably goes to b4 to pressure the weak black pawns, allowing the bishop to develop thereafter.  

A fidget spinner would do.

Very insightful. And I didn't realize that blunders, mistakes and inaccuracies were correlated with skill levels. Thank you!

I appreciate your insight. Thank you

😅  reassuring. Thank you!

 Yes, you should not worry about the moves computer labels as inaccurate. Worry the ones it labels as blunders and try to understand why they are blunders. Of course this is quite rough division, and to see more nuances you could look at the actual evaluations: if the best move is evaluated +0.25 and second best +0.20 there's hardly any difference at all but if the difference between the best and second best move is several centipawns then you should certainly try to understand why this is.

I believe a4 threatens 2. axb5 axb5 3. Rxa8 Qxa8 4. Qb4 winning a pawn thanks to a double attack against b5 and d4 but this threat is quite easily parried and it's quite unlikely that a4 is much better or worse than other natural moves (in such a case even the computer may easily change its preferred move if you let it think little longer).

The important thing for you to understand regarding this position is that white's main problem is developping the queenside because the queen in d2 currently blocks the most natural development route for both your bishop and your knight (you have probably done something wrong earlier in the opening for this to occur) . Therefore any natural queen move trying to correct this situation like Qg5, Qe2 or even Qd1 should be considered quite seriously.

I don't think that this is the reason.

white is fighting for the dark squares. After 12. a4  see black's dark square bishop is blocked by his own pawn. The idea for 13th move for white would be to play 13.c3!. White's dark square bishop would be better than Black's bishop. Secondly, There would be weak pawns in Black's camp.This is the perfect time to play a4. I hope you know the concept of minority attack to create weakness and open files.

bump

Where Black has played ...a6 and ...b5, White's a4 is a well known priyome, a strategic device that often works well in a particular pawn configuration. That is not to say that it is always the best move, or even that it always works. But it is always a move to be considered.

A great example of the priyome in action was Najdorf's win over Fischer at the 1966 Piatagorsky Cup, the only time Miguel defeated Bobby.

I might play 12.a4 based solely on developing your pieces quickly.

White has 3 pieces in the unemployment line. On a1 b1 and c1.

With developing your pieces as your only strategy you still want to develop all of your pieces.

In order to develop the a1 rook you could play a4 or you could over the next zillion moves develop it to some square to the right of a1. You should then realize that developing your a1 rook to a square to the right of a1 will take way more time than just playing a4.

12.e5 moves the same piece twice when you still have 3 pieces on a1 b1 and c1 undeveloped.

Developing the Knight on b1 to a3 means you need to play a4 also since if you don't play a4 then Na3 looks like the knight has no future but if you play a4 before Na3 the Non a3 has a future.

Just concentrating on developing pieces quickly is a main fundamental of chess.

I would say it is the most important goal in the opening.