It's not really necessary, but it can make some situations a whole lot easier. Some of the pulls in MGT comes to mind, not to mention the third boss. Still, come WotLK, you'll be hard pressed to find a group combination with no CC. Shamans get hex, druid root now work indoors, mages have poly, locks banish, hunters trap, rogues sap, priests have shackle and that new intervention-like spell, even ret paladins have CC now. Basically you can't get a non-cc group unless you're rolling with 5 wars :-)