When doing roulettes, if your HP is dipping very, very low you either have an extremely good healer or an extremely bad healer. You don't know which until you die and the group wipes. So it is a gamble.
If you clemency and the healer is good, they just get to DPS some more. If you don't clemency you get a a more efficient run. The problem is with bad healers. If you clemency with a bad healer you save a wipe, if you don't clemency you wipe.
My personal experience is bad healers outnumber good healers and the only place you don't want to be is wiping. Plus they'll complain no matter what you do. Use clemency and they'll complain that you should be DPSing, trust them and don't use it and they'll scream it is your fault when you wipe.
