I've always liked the idea that as a tank, my health bar is out of my hands and in the healer's. This isn't to say it's not my responsibility to pop cooldowns, but that reacting purely to damage coming out is poor play. I have CDs I use depending on the packs I pull and how I expect damage to hit. It should be basic, expected play to use CDs for packs, bosses, and to plan these uses.