Since the main play I engage in is bondage, I do this precisely every time; and ANY person I play with, I insist they do the same (e.g., whether dom or sub). My last couple play sessions with guys from RM were at a bondage club rental space in LA, and the staff literally checks on you a couple minutes after the session is over (by knocking of course LOL) so the safety factor is very high. But this is a non-negotiable for me in every encounter, even if it's with someone I know well and have played with a lot. It goes just beyond the safety of harm from the other party; it's also the idea of - what if I have a heart attack while the other guy is restrained, for example.