Question about a move

[TexAg06]

I was playing through the game Smyslov-Nunn 1982 (see full game here: http://www.chessgames.com/perl/chessgame?gid=1103145) and came across the diagrammed position below.



Here Smyslov played 8.Bb5, and the game continued 8...Bd7 9.0-0 a6 10.Bc4.

Could someone help me understand why Smyslov played the bishop to b5? Perhaps he wanted to capture the knight to inhibit an e5 advance (I don't know if I like that idea), but black can play Bd7 (as he did in the game), which looks like a natural enough square for that bishop anyway. After 9...a6, Smyslov has to move the bishop back to c4 but it seems like black has been given a free tempo to play a6. Why not just put the bishop on c4 initially with 8.Bc4?

Forgive me if this is a dumb question.

[Vempele]

Bc4 invites a d5 break, e.g. 8. Bc4 g5 9. Bg3 d5.

[TexAg06]

That makes sense, I didn't think about that.

[jewbinson]

Is Bd3 also okay instead of Bb5? If the response is e5 then just ignore it (because d5 is asking for f5)

[Vempele]

It turns out my line is just bad for Black, but he can instead force White to sacrifice a piece by 8...Nxe4 9. Nxe4 (Bxf7+ is rarely ever good in these spots, especially with Black having castled) 9...d5 10. Bd3 dxe4 11. Bxe4 f5. Here I only saw 12. Bxc6 and didn't realize White still can't save the bishop.

[computer-assisted]Best is 12. Qb3+ Kh8 13. Bxc6 bxc6 14. O-O with equality. Black can't avoid a perpetual without making some otherwise pretty useless moves; those tempi will give White enough compensation.[/computer-assisted]

As for Bd3, I'd rather not have the bishop on the d-file when it opens.