You never want your second act or the whole movie to just be this relentless march towards its goal. You want things to take the audience by surprise.

In live-action, writing, production, and editing happen in discrete stages. In animation, they overlap - happening simultaneously. This allows a real dialogue to occur between the writer, the director, the actors, and the editor, and it makes the writing process a lot more collaborative and a lot less lonely.

In terms of writing characters or stories, at least initially, there's no difference between live-action and animation. A good story is a good story, whatever the medium.

I like to begin every screenplay with a burst of delusional self-confidence. It tends to fade pretty quickly, but (for me, at least) there doesn't seem to be any other way to start writing a script.