It was tactical, actually - we'd be pushing pawns to prevent or facilitate various plays. I think a4 was protecting against some tomfoolery with his white bishop, and a6 preventing mine from checking on the diagonal - I think he had moved d3 to set up an attack, and that's why I moved c3 - block the d4 space. Also, I had my white bishop on c4 for a while - the pawn there now was defending it when Black captured with a knight.

I mean, stuff happens to pawns. I wasn't going to worry about it while I had the initiative.