tanks not using cooldowns?

[Reinha]

Or... You can just heal... My cooldowns are for when you go stupid and I'm getting dangerously low on HP and you're still DPSing the mob instead of doing your job and healing me.

No no no no.... Don't sit on your cooldowns. A tanks job is to direct all the damage to themselves and then mitigate that damage. You are doing only half of your job and slowing down the run. An example of how proper use of cooldowns helps you during emergencies:

You have 25k health and you take 1k damage per second from a pack of mobs. After 20 seconds you have 5k HP left and assume you're in trouble, so you pop a 20 second cooldown which reduces damage by 20%. At this point (5k HP) it can only prevent 1k HP before you hit the dirt and you only get 6 seconds use from the cooldown. You die in 26 seconds and waste 14 seconds of a cd. If you had popped that same cooldown on pull, you would have had 9k HP left after 20 seconds as opposed to 5k HP, and it would take you 29 seconds to go from full health to dead. A noticeable difference and it's only with one cooldown. You could use more in one pull because most only take 1.5-3 minutes until they're back up.

So even in emergencies it's more useful to have popped a cd or two close to the beginning of the pull instead of saving them. Outside emergencies you are making the healer's job easier with good cd use and giving them time to dps more, which in turn makes the fight last a shorter time and prevents damage that way. And you get to finish faster! No matter the situation, you should always be using your cooldowns from the start except the ones that provide immunity to damage.