On the XC bike it stays up for 95% of a ride, drop it out the way if I find some drops/jumps I fancy having a quick go on
On the FS I used to leave the saddle up as much as I could, the sensation of just about to go over the bars got old though trying to ride stuff with more sudden gradient changes (eg multiple sections of stairs). That and wanting to be able to learn to ride/absorb 3' drops. I bought a (5") dropper post as my frame only has about 3" of saddle drop with the seatpost cut as much as possible, and use it quite a bit, a lot of those times may only be dropping it 1-2" though, so I can still pedal reasonably effectively
As above I could mince my way down stuff, but its more fun to drop the saddle a bit and try jumping off stuff, moving weight around a bit (quickly) and going faster

