2nd sequence question

Maybe this functions importance is right under my nose, i dont know.
But 6 years later and i still cant figure out what this function is good for?

Can someone explain

And a few more ABC questions while im at it.
"poly pressure" and "exclusive"......havent figured these out either.
The manual is way too vague.

Lampdog, thanks....the link is very informative.
Just what i was looking for.