legit question, steven. do you only let them do the hi rep back off sets after they have stalled?
high reps do a couple things in my mind that are very positive (again, mostly me, sample size N=1).
reinforce technique and cues under fatigue. it's real easy to figure out your own particular weak points and efficient ways to move through them when you're doing light weight for reps while fatigued. it's ver easy, in these cases to indentify and correct your own "20%" slop.
thing two: confidence.
very often after working up to a significant number, let's say the goal was a triple at a set weight, even if the tripel was a brutal struggle, taking a chunk of weight off the bar and then cranking out a set of ten can be confidence inspiring. for some folks, they'll quickly be hitting for sets of ten weights they had been struggling for 5's not many weeks before.
does this make sense?