1 - Yes I do them, only I have always done them for reps vs. 1RM's
2 - Always check the low back; if there's any rounding whatsoever in the movement, I have them return to the start. Please, don't force the issue here!
3 - For certain populations, yes. I would love to go into more detail here, but just wait for Eric and I's article called "Lousy Leverages"...it will explain everything