Why waiting moves are ( sometimes ) great

I was wondering why my computer sometimes suggests waiting moves. As an example, in the position occurring after 1.d4 Nf6 2.f3 d5 3.e4 dxe4 4.Nc3 exf3 5.Nxf3 g6 6.Bf4 Bg7 7.Qd2 00 8.000 Nc6 9.d5 ( gaining space )  Nb8 ( only option as 9...Nb4 10.a3 and 9...Na5 10.Nb5 with slight white advantage ), my computer now suggests 10.Kb1 (diagram).

Why is this waiting move better than the natural development move 10.Bc4 ?

Let's look first at 10.Bc4. Obviously, black wants to generate counterplay on the queenside, so 10...a6 is the obvious choice. White can not block this by 11.a4, since 11...b5 would open up the file for the rook. The alternative 11.a3 is surely better, but again allows black gaining space with 11...b5. So playing 10.Bc4 allows black to counterattack on the queenside.

Is this counterattack possible after the waiting 10.Kb1 ? The immediate 10...b5 11.Bxb5 is certainly not possible, so black needs to prepare this advance first. He can do so in two ways : a6 and c6.

The first option 10...a6 is countered by 11.Be2 (diagram)

The thematic 11...b5 is now answered by 12.Ne5. If black continues attacking like a madman with 12...b4, then white finds a great spot on the rim after 13.Na4. A knight on the rim is often dim - as the saying goes. But this is not the case here, as the white horseman can lateron move to the outpost c5, which is not guarded anymore by a pawn. Charging away the knight from his outpost with 12...Nbd7 is deadly, as c6 is not guarded anymore by a pawn.

The other way of preparing b5 is 10...c6, but now white delves deeper in enemy territory with 11.d6, followed by 11...exd6 12.Bxd6 Re8 and only now 13.Bc4 (diagram).

Black's counterattack 13...b5 is not to be feared after 14.Bb3 as 14...a5 is countered by 15.Qf4 and white's pieces are everywhere. The option of 14...b4, chasing away the knight, is not available in this position with the bishop on d6. So black has only 14...Be6 15.Bxe6 Rxe6 16.Qf4 with an equal game.

Lessons learned ? As an attacker, don't allow the defender a counterattack by exposing your pieces to rapidly, without them having an immediate threat. Consider a waiting move instead, urging the defneder to choose a defnese first - then attack. However, guess this approach is not the preferred choice for Blackmar Diemer gambiteers...