1. a3 1247 36.5 % 24.5 % 39 %
1. f4 16877 35.5 % 24.5 %
40 %
It has better win percentages than my beloved 1. f4, which is a fine weapon. Even Fischer won with 1. f4 against Smyslov. But of course, it is bad too.
1. a3 gives White transpositional opportunities. Chalking this up to winning a piece vs. a mate in one is a silly argument, since this has nothing to do with that. It is a waiting move.
What is wrong with 1. d4 and 1. e4? Nothing! But, you do give Black targets to attack. With 1. a3, you have not yet revealed your cards. It is simply a good ,waiting move.
I think it's a perfect analogy. Surely you can see that I was exagerating to make a point? What a3 gives up is very very small, but it still gives something. Play 10 more "good, waiting moves", and see what happens. The best you'll get out of it is transposing into an opening where it's useful, and if black is a good player he'll avoid that. At least f4 is based on some logical principles.
Playing 1.a3 is perfectly valid, but expecting a reverse open game is not the point. White must know WAY more than just that.