These are all nice ideas but what is not mentioned is how the level of the mob compares to the cleric. Here is a list that illustrates approximate % of stun failure (it is not exact calculations rather the table is based off my experience when playing a cleric):
Red = 99% stun resisted
Yellow = 75% stun resisted
White = 50% stun resisted
Dark Blue = 40% stun resisted
Light Blue = 20% stun resisted
Green = 10% stun resisted
Gray = 1% stun resisted
Now lets say and you are experiencing in the latest high level zone full of reds and yellows and you have an agressive puller who pulls 3 red con mobs to your group and you have no crowd control but there is 1 cleric in the group. Do you think it is a good idea to cast an AE stun spell?
Now lets say you are doing some task solo and a boss mob who cons red and 2 guards that con light blue. what do you think will happen if you cast this spell?
Now lets say you are in a zone experiencing with dark blue and light blue cons. Does it look like an AE stun may be a bit more useful in this situation considering the confidence level of the stun actually landing is higher?
Assuming the stun is successful do you have the armor/stats capable of allowing you to withstand a beating long enough to live? Remember your a cleric not a Paladin.
Would a single target stun be more useful in any of the above situations?
Of course there are other considerations like is the mob(s):
immune to stun
immune to root/snare
taken any HP damage
taken any other type of agro
social to fellow mobs (intelligent)
So before you even consider throwing a stun consider the mobs level in relation to yours and you may live to tell about it :)