[ Thanks to steve
hill for this link. ]
“Animated films (and even live-action films with animated
special effects) involve quite a bit of work for every second you
see on screen. This creates a production problem in terms of
reduced flexibility. You can’t experimentally shoot a shot over and
over again from different angles until you’re satisfied. Instead,
you need to know exactly what you intend to produce, and then
produce that.“But how do you figure it out? At first, of course, you have the
ideas in your head — you see the film like a little movie
running inside your mind. But that’s deceptive and difficult to
quantify. So we have steps for moving the idea out of your head and
onto paper (and/or into computers).”