In most PvE instances, specially low level ones, CC isn't really a factor - in fact I'd say the most use CC skills ever see is in PvP :P So my two cents is, don't count on it, don't expect it. This matter is further made obvious by the fact that the best CC skills are usually WHM/BLM sleep skills, and they're rendered useless by most tanks since their aoe enmity generating skills wake up the mobs...
I personally only ever bothered with sleep and other CC skills when the tank/healer were so bad I could foresee numerous wipes incoming if we didn't take one mob at a time.
