The bishop, being a long-range piece, is just as effective on b3, and it's now protected by the pawns and out of range of the pawn advance ...d5, which Black may wish to play later when the square is better defended, and with the bishop still on c4 White would be forced to exchange pawns, which he might prefer not to have to do.

On c4 the Bishop is loose and White has to watch out for combinations with ...b7-b5, ...d6-d5, or the fork trick with ....Nxe4. Both 7 a3 and 7 a4 are options.

A prophylactic move as Nimovich would say.

Puts pressure on f7 because of a future threat of f5.

Black's thematic counter play comes from ...b7-b5. On b6 the queen would block the backward b-pawn. ...Nc5 also clears d7 for the f6-knight which may need to go to d7 after a future e5 by White.

But Black could play 12... Nxc3 13. bxc3 Nxe6.

after 12...Nxc3 13 bxc White has an half-open file for the a1-rook, and it becomes very hard for Black to generate queenside counterplay.

Bobby won 60%, drew 30% & lost 10%. He survived a lot of times.

oh yeah!

Threatens 20. Ne5+ winning the queen.