Why does Caruana push 11.h3 against Aronian?
[fen ""] [startflipped "0"] [startply "20"] [title "F. Caruana v. L. Aronian, FIDE Candidates 2018"] 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.d3 d6 9.Bd2 Bg4 10.c3 d5 11.h3 (11.exd5 Nxd5 12.h3) Bh5 12.Qe2 Rb8 13.Bg5 dxe4 14.dxe4 h6 15.Bc1 Bg6 16.Nbd2 Nh5 17.Nf1 Bc5 18.g3 Kh7 19.Kg2 Qe7 20.Bc2 Rfd8 21.b4 Bb6 22.a4 Nf6 23.Nh4 Qe6 24.Bd3 Bh5 25.g4 Bxg4 26.hxg4 Nxg4 27.Nf5 Nxf2 28.Bc2 g6 29.N1e3 gxf5 30.exf5 Qf6 31.Qxf2 e4 32.Rh1 Rd6 33.Bxe4 Rg8+ 34.Kf1 Ne5 35.Qf4 c6 36.axb5 Rg5 37.bxa6 Qd8 38.f6+ Ng6 39.Rxh6+ 1-0
Caruana's 11.h3 does nothing I can see but to kick Aronian's bishop back to h5, seemingly a better square.
Yet Caruana wins the game, against Aronian, no less. So has Caruana's 11.h3 actually somehow helped?
Is Caruana's sole purpose to make Luft without loss of tempo?
But this seems doubtful. Why make Luft so soon? Aronian still has both bishops, after all; so, if the purpose is Luft, then how can Caruana already know that the h-pawn will have been the right pawn to push? (In the event, if Luft is what Caruana wants then he soon gets plenty of it. Aronian trades the bishop for all three of Caruana's kingside pawns!)
Perhaps Caruana is dreaming of an eventual g4 and a pawn storm against Aronian's black king. But from this position? I see no sign of it. Do you?
MOTIVE BEHIND THE QUESTION
Though Caruana's game against Aronian does indeed interest me, my question has a broader purpose. Opponents sometimes play moves like Caruana's 11.h3 against me. I do not understand h3 (or h6) when they play it any more than when Caruana does.
I understand kicking a knight by h3. I also understand kicking a bishop by a3, insofar as the king is not near. But kicking a bishop by h3? If one does not mean to follow with g4, then why bother?
I would like to understand.
If you wish to know, Stockfish slightly prefers 11.exd5 Nxd5 12.h3, which is not wholly dissimilar to Caruana's play, so apparently Stockfish understands Caruana's thought. Unfortunately, I do not understand it. If you can illuminate the push of the rook pawn in a position of this kind, I would appreciate it.