I don't see much point in opening a file on the side of the board where my opponent will be dominant. I just leave the Pawn at a2 and use that tempo elsewhere.
subtle move choice in closed sicilian for white , advice from advanced players

the problem is, if you dont move a pawn, black can get both b4 and a4, and then the threat of a3 along with the g7 fianchetto is very annoying. moving the a pawn lets you contest the file temporarily at least.
Well I know GM Patrick Wolff once annotated 1 c4 e5 2 Nc3 Nc6 3 g3 g6 4 Bg2 Bg7 5 Rb1 a5 ! saying it was the only way for black to keep equality. Okay.
And I know GM Vlastimil Hort always answered ... Rb8 with a4 in the Closed Sicilian. But I don't like it. What is good for black is not necessarily good for white. (1) Especially annoying is ... Nd4 when c3 might be met by ... Nb3. (2) Another positional plan for white is a3 Rb1 Bd2 and b4 , playing a4 gives up on this option. (3) Finally, it's sometimes possible to play a3 _after_ black has played ... b4.
So I almost never play a4. I would rather use this half tempo elsewhere and play a3 only if the a1 rook can't reach the kingside.
So, i have played the closed sicilian (specifically, 2.nc3 3.g3 with intent on playing the be3 qd2 variations) for some time but one stylistic choice with subtle consequences whose differences have eluded me is when to play a3 vs a4 agaisnt the rb8, b5-b4 queenside expansion with the kingside fianchetto.
Sometimes, it seems the positions end up near identical with white trading the b pawn once, getting the a file usually going nd1, but what is your thought process when deciding to play a3 or a4 to slow down the pawnstorm (or even not move the a pawn and allow b5-b4). Is there something specific you aim for, are waiting to see when choosing one or the other?
i seem to do slightly better when i try a3 over a4 and im not even sure why lol.