KID fiancetto variation - reason for c6 after Nd7 I've noticed that when black goes Nd7 in the KID fiancetto variation, then often he follows up with c6. What is the main reason(s) for this? Especially, I'm asking this question as often the d6 pawn afterwards becomes subject for attack by white. First I thought the reason was mainly defensive to hold white knights away from b5 and maybe even d5, but I don't really see this being such a threat. Then I figured the reason for c6 was do go d5 at some point, but rarely does black indeed play this move, so I'm unsure as to why black usually does go c6 and thus creates this target on d6. 

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1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.Nf3 O-O 5.g3 d6 6.Bg2 Nbd7 7.O-O e5 8.e4 c6 ( 8...Re8 9.h3 c6)
First of all, to sit back and wait isn't a good strategy for black, as white has many useful moves to make: h3, Be3, Qc2, Rfe1, Rad1. If white can get these moves in with black doing nothing, white will be clearly better.

So black has to look for counterplay. Most of black's options involve c6 to activate the queen on the d8-a5 diagonal. If you absolutely don't want to move the c-pawn, then one of the few options left is to play exd4 followed by Nc5 and a5. This is playable, but not popular, as white can place an annoying knight on b5, see Giorgiev vs Ilincic, Belgrade 2000.

Black can also try to play exd4 and Nc5 without a5 (instead Bd7, a6, and so on). The game then can get sharp, but current theory says white is comfortable.

In summary: Black plays c6 to get needed counterplay. The other options to get counterplay aren't quite as attractive.