Why the center?

Yes, 1 b3 controls the center, but it allows black to set up a solid block on e5 or even d5, so it doesn't offer the same chances of advantage of more aggressive first moves. 1 Nf3 though is very flexible as that knight being there is useful in most openings.

Certainly that's one way to look at that, but in for example 1 e4 g6 white's center is a little more power usually doesn't fully equalize. But in fact in some weird cases it's an actual mistake to set up (or more often advance) a pawn center if the other side has his rooks on the center files and your king is still on e1. Then some sacrifice might be strong, destroying your center and opening up all those files for a big kingside attack.

  If white makes 1.b3 it is very tough to play with black without any theoretical knowledge and memorizing countless variations and stuff.  So with b3 and then Bb2 creates alot of very uncomfortable situations on a1 - g8 diagonal.  So keeping dark square bishop (for  Black ) is very important.  main idea of whites bishop on a1-g8 is to hit center squares with pawns.

I completely disagree about it being hard for black. Without any book knowledge but a good knowledge of strategy, black will just set up a modest center (I don't think he should try to claim an actual advantage until later), get out his pieces and will be fine. One b2 bishop doesn't equal kingside attack, especially if black blocks it with ...e5.

I have played this opening for a pretty long time, so I know the variations, and other stuff. I do agree with you though

i played both pawn at the centre and the centreles pawn position to experiment which one is good or bad,then i came to know that centreless pawn position leads to bad position even though i won that match i think centre less pawn leads to bad position!

I used to play the Nimzo-Larsen, to give 1. b3 its proper name, a couple decades ago, mainly to avoid opening theory.  It is OK.  I think there is better.  Given the statistics on who plays it and when I think most titled players agree with me.  It does not put white at a disadvantage but it does not preserve his advantage. The better player should still score more but it will be more difficult for White to win.

BTW Nf3 in its many subsequent forms (Reti, English, or other transposition) is a more respectable opening.  1. Nf3 immediately addresses the center.  1. b3 does not, it takes two moves and that is where white tosses much of his initial advantage.

I rarley play here,I am acctually 1300 and I play people my strength, they may also be going easier on me because they think im weaker