-if the opponent's guard bar is low enough, you want the followup as fast as possible. for instance, in most wild throw -> things-and-three-sidewinders combos, if you end with jx->vv, the followup is actually black beat (your opponent might not tech anyway, heh) (which is why you want to end those combos with bandit revolver instead)
-if you do a grounded vv on johnny, the followup is always black beat. but this isn't true for the air vv, for some reason. lol johnny