As opposed to live-action films where you shoot the footage first and then cut it all together, in animation you record the voices first, then animate the footage. This allows the animators to match the animated performance of the character with the voice.
I think of two of my favorite voice performances in animation and wonder what effect they had on their respective animators. One is Jane from Tarzan. Minnie Driver's incredible performance allowed supervising animator Ken Duncan to have tons of fun with her on-screen. And perhaps my favorite voice performance in animation to date would have to be Kronk from The Emperor's New Groove. Patrick Warburton is out-of-his-mind fantastic as Kronk, and supervising animator Tony Bancroft had a field-day with him.
We have also been getting some great performances from Dan and the rest of the OZ cast. The animation studio is working to get some iconic magic like the above mentioned films as well. It's due out in 2012... hmmm, isn't that when the Mayan calendar runs out... let's hope it's releases earlier in the year, before any of that takes place.