I've read arguements that say always go with coating and others that say coatings are no longer needed as much now since everyone shoots with filters that are already coated.
If I remember correctly, the non C had problems with light flares. The coating it supposed to almost eliminate (or at least reduce) this.
After looking at a lot of lens for my other camera (Nikon 35mm), and they were ALL coated, I figured, you can't go wrong with it. I doubt it would hurt the final image, and the $ difference isn't really all that much anyway.
Myself, I bought the "C" lenses.