1.a3

I played 1. a3 for years, intending to head for a transposition into a colors-reversed opening with a tempo more.

For instance, if the opponent answers 1. ... e5, then play 2. c4 with a reversed Sicilian (in which the a-Pawn often plays a constructive role... eg: Najdorf or Scheveningen). 1. ... d5 can be met with a reversed Benko, or reversed Modern Benoni, or even a reversed QGA; since the a-Pawn can play a constructive role in all of these openings.

The point is not just transposing into a known type of (colors reversed) position with an extra move... the fact that a3 has already been played rules out some of the critical lines that your opponent might otherwise have played. The most aggressive and double-edged White systems against the Sicilian are simply unplayable as Black against the reversed Sicilian, for example.

The true brilliance of 1. a3, is that if 1. e5 , you can enter into a Scandinavian with White, while up a tempo!

I like the idea of 1 a3 and then play my favorite defenses in which the a3 move will probably be useful. That is a bit of compensation. 

However, what about 1 a3 g6. Seems then now white has no compensation for playing 1 a3 and is playing as black full blown.

Play 2. g3 and head for a reversed KID Panno?