I often think that the careers of folks who started out as Daily Show correspondents is illustration of why supporting actors are so important. Take Cedar Rapids, in which Ed Helms is clearly the supporting actor in his own movie:
Without that slight blank, cheerfulness, though, the other characters wouldn't have the catalyst they need to turn in what looks like a reasonably amusing series of performances. On the opposite end of things, John Oliver is just a genius of disruptiveness as Professor Ian Duncan on Community:
His character doesn't fully gel with the dynamic of the cast, and his persistent loopiness might be too much if it was on the show all the time (I think Community's achieved a nice balance, after basically ignoring the character for most of last season). But it's excellent leavening, a reminder that the characters have turned a lot of weird things into a fairly consistent level of normal, but that the world around them is stranger still. It's beautifully proportioned.
I know everyone wants to be a star, for both one-off pecuniary and consistent-level-of-employment reasons. But artistically, there's a lot to be said about providing either the canvas or the splash of color that makes the work pop.