I don't really use it since my fingers are already all cluttered up and I don't have fingers to spare to hold R1 the whole time. Also, the game tends to move the camera to give a wider view of the fight which aggros enemies when they come on screen. I don't really see the need for it very much, and since the combat was designed without the need for it, its not that useful like it was with the classics where lock-on was everything for combos and moves. As for lock-on with Vergil, that enemy that needs to be struck with a summoned sword to be able to hit and kill, screws up the lock-on. It makes Vergil attack the opposite direction and defeats the purpose of lock-on. All in all, I hardly use it. I only ever use it when there are less enemies or when I am in Training.