In my opinion, in my play style, I absolutely need CDs for trash about 80% of the time. The reason is I do big pulls, lockout to lockout, and without the mitigation my oncoming damage is greater than incoming heals, even if heal after heal is cast. The exception is drk, at least for me. After I have the group, I pop blood price and dark arts abyssal drain spam, once blood price falls off I pop a CD. I live by a tanking standard that the only reason my healer should not DPS, is if they CHOOSE not too.