I'm in the 20RM club for both deads and squats.
But when I do them it is for a specific reason.
1) I only do this once every 6 weeks in place of my regular dead or squat workout.
2) I do no other assistance exercises that workout
3) I do it with roughly 70% of my max
4) I do 20 sets (after a warmup)
I have found that when I do this, I can break through any barrier I may be having. It also is a shock to my CNS that is done intentionally, usually before I make the move up to a heavier cycle of working sets.
Finally, it is my way to commune with God as you may understand him/her. Around rep 15 of the second set, I swear I see him.her and I just keep doing what I am told to do by him/her.
I say this all with the caveat, that it is not for everyone, and you need to know your body better than anything, and you need to have some serious experience under your belt.
The old timers called these "Milk & 20's" because they would drink a glass of milk immediately after the 20th rep.
B-
One of my offseason sessions once a month was to superset 20 rep squats with 20 rep deads. Lots of fun...and vomit.