The drill will work no matter what technique you use to throw inside/outside.
It’s no great revelation to say that working the corners by being able to hit your spots inside and outside is a critical skill for fastpitch softball pitchers. The easiest pitches to hit are the ones down the middle, so once you can do that reliably the next step is learning to never throw there again (except maybe on a 3-0 count).
Of course, it’s easy to say “you have to hit your spots.” It’s another thing for fastpitch pitchers, especially younger ones, to be able to do it.
