Basically, it depends on whether the transition needs to be sharp or smooth…(not very helpful, I know).
I’d recommend actually doing the opposite of what Kent does in those 4 instances; so using ‘Smooth Mask’ when he doesn’t and vice versa. (I have done that myself, because I was asking myself that same question…)
I’m sure Kent can give you a much better explanation, but I hope this at least helps a bit.
