Rook Pawn Forward

When I run analysis for my games and a player is setting up a fianchetto early, I've seen the computer saying moving after move for me to move my rook pawn forward. Like this:



What's this all about?

a7-a5-a4-a3 and it's not clear what to do with the bishop b2

Guess it seems strange to me to be spending opening moves like that which seems to break all the standard ideas. I'm moving a piece multiple times, I'm not fighting for the center, etc.

But in this particular position the center is yours, your opponent spent a lot of time so you can play such a move to annoy him.
In addition your rook becomes more active.

Usually when on player pushes their rook pawn, the other can stop it with h3/6, so it's not a big deal. When a player is has a bishop fianchetto, though, they can't stop the pawn that way, so they usually have to either ignore it or play h4/h6, which can be a very weakening move. Since it takes several moves to get the rook pawn up that far you would usually only do it when you are ahead in development, have the center or have all your pieces well placed.