User blog comment:Staw-Hat Luffy/Why Kaido?/@comment-4754162-20130206014519

I am of the opinion that Kaido was choosen because there is a flaw in his army that Law is trying to take advantage of.

While its not entirely sure yet but I'm taking a guess that SAD is required to sustain the strength of his artificial zoan army. With the supply of SAD interupted, his army will be greatly weakened, this is the flaw that Law is trying to exploit.