Preparing ...Bc6 and ...Nd7 in order to improve the bishop and step up the pressure on the e5-pawn.
In contrast, 1...Nb4? runs into 2.Nd6+! cxd6 3.Qxb4 with a clear white advantage – Karpov.
After 4.Nxd7 Rxd7 Black has a long-term edge thanks to the weak e5-pawn, so White opts to transform the position.
White keeps the d5-square under control, without worrying about the doubled c-pawns.
From now on the ...d6-d5 break can be discarded, and Black is also suffering from a backward pawn on d6.