If the issue is healers running OOM and unable to spare a heal for your pet one of two this is going wrong:
A: Your raid isn't aware enough and is taking way too much avoidable damage, or tanks are not using teh correct CD's to mitigate damage that has to be healed through.
B: Your healers are badly geared or just not that good.
You should never have any issue with your pet dieing, if your anything but destro, it will be in melee getting incidental AoE and splash healing, more than enough to keep it alive. If your destro, your pet may take more damage but I don't run as destro so I have no experience with that. Healers should heal pets as well as players however, even if it's taking 20%+ of the damage you take. If they bitch about it then they are just not understanding how a warlock played and should be educated by yourself.
Always use it, it was given to all specs baseline for a reason. If the healers are really struggling in keeping you and hte pet up, maybe look at not glyphing it? I dunno though. Just makes me ask questions of your healers rather than you as a warlock using a class ability *shrug*.