There's a bunch of uses, mostly it's if you don't have OD to begin with, or you have too much health for a combo, or, it's if you just don't want to use OD in the first place.
On the questions that you asked, my pressure is non existent, nails/3C, and combos. A good way to get seals, I found, was 5D ch then 2D j.D c nail and 6D. But all of those of course are really bad and I need to devote a day to work on them