Stun that get's in the way of my own rotation as PLD; same when I ask my Monk friend not to use his stun skills so I can manage the mobs abilities, and he can dish out DPS.
First stun (not counting low-lvl dungeons) 6 sec, next 3, last 1, then resist. When a WHM uses Holy, The first one will be used for about 4sec, then next one will overlap, then third one.. hmm.
So for me it's more about the nice damage it does, when everyone is safe from harm, it gets the mobs to be killed faster.
I understand that Healing can be boring for some. They can DPS when everything else is covered, not counting if other ones knows what they are doing to complement them.
Like my HG Macro that tells my WHM mate he can go all out since I have 10 sec of invulnerability, and he saves his benediction right after it.
No matter which class/job you play, it's how you know the other one's roles and then you can fit in, for everyone to get that kill down and instance completed.
The more you play all role, the more it makes you get into their shoes, and then you can stop bashing if you are only DPS for example.
Everyone will make mistakes (Me first ^^) ; all that comes down to it is that if you ended up with a success, within the time limit.
@Nyne: Love your sig - so true!!! ^^