+1 to everything Scut Monkey said. Another advantage of using a starter is to help control esters and/or beer flavors. With my hefe's I've been doing a proper starter with the calculations at mrmalty.com and not getting the flavors I want, so now I can fiddle around with the pitch rate to see if I can get the flavor I want by "beating up on the yeast count."
Bottled: Oatmeal Porter, Double Chocolate Chipotle Porter
Kegged: IPA, Red Rye