Sicilian Defence, Dragon Variation [FEN ""]
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 g6 6. Be3 Bg7 7. f3 O-O 8. Qd2 Nc6 9. O-O-O d5 10. exd5 Nxd5 11. Nxc6 bxc6 12. Bd4


What is White's plan &amp; idea behind 12. Bd4 move?
Something that instantly stands out to me is that 12. Bd4 challenges black's strong fiancettoed bishop.

Black must submit to trading pieces or weaken his bishop.

Also,12. Bd4 removes pressure from the c3 knight. This piece is in a bit of a weak position, especially since one of its defenders is a pawn next to the king that we don't really want to move, and definitely don't want to double up.

Finally, 12. Bd4 could help white control the d-file. Black's queen could step out of the way much more easily and allow the d1 rook to push the d8 queen off of the open d-file. (For example: Knight takes knight, queen takes knight, bishop takes bishop, rook takes bishop.) The queen is also free-er to move along the "up-and-to-the-right" diagonal.



Regarding other future ideas:

A move like Bc4 might be in order soon: it develops a piece, unites the back-rank rooks, attacks a strong but weakly-defended piece, and has the chance to participate in a kingside attack, eventually. It also protects the hanging a2 pawn.