If by RNG you mean a mild annoyance then sure whatever. The person with torment has to heal the tank and if both healers get torment you have to triple soak or pop some cooldowns. If you suck at reacting to stuff though sure 3 heal it.
Meh, we always 2 heal our main run but 3 heal our alt run. When progressing there's no reason not to 3 heal, its safer and can save a few wipes.