It can really slow you down sometimes. I'm running 3 teams, 5 shamans, 4 locks and a priest, and 4 Mages and a priest. In Shadowfang Keep, the curses would slow me a lot on the shaman team, because without a way to remove them, I just waited them out before going after boss kills that were already a bit dicey. On my mages, they were not a problem. I still couldn't get rid of poisons, but between the priest dispell and the Mages decurse, I could get rid of the troublesome ones. I also run with a buddy sometimes, and being able to dispell roots on the tank is critical to him being able to hold aggro.

If I was going with 4x warriors, I'd go with a Shaman if only for Windfury Totem. And Chain heal will probably be pretty good. The cleansing totems make quick work of poisons, etc.

Unless you run a 4-5 class team, you just have to live with the tradeoffs of which buffs/debuffs each class brings. For leveling I like to keep things simple, and have 1-2 classes at a time. At 60 I will experiment with a multi class team, and having all the spells available will make it a bit better to choose the optimal makeup.