Do you mean like when you mean like sometimes I use the velocity to have a sample come in soft to loud, but with after touch you can apply a filter to it so when I hit it gradually harder the sample will like "open up" or damper?
no, nebulous, what you're describing is velocity filter modulation, which you can already do in os1. in os2, it's VELOCITY>EG in the filter screen.
aftertouch is exactly what it sounds like - a readout of your pressure levels after the note as been registered. i imagine this to be best for bass, where you could set a sine on 1 pad and simult a square on another. set aftertouch to low filter on the square, hit a pad and tremble your finger for a warbling, talking bass.
but holding pads down all over the place could put me off a bit.
so i'm to assume you never use the NOTE ON function? if aftertouch is very useful on a keyboard, why wouldn't it be just as useful on an mpc?