Regarding pre-editing:

Let's say you're a film director working on 35mm film. If your movie is 90 minutes long, you'll probably shoot 16 hours of footage, which you would craft in the editing room into a 90 minute film.

Because rendering is a time-consuming and CPU intensive process, you'll want to "pre-edit", perhaps more commonly known as an animatic. In pre-editing, all of your shots are blocked out with their (time) lengths established before any animating is begun. So if you know your shot will only 4.5 seconds long, you won't render out ten seconds to later decide that you only need half of it.

Don't know if that makes sense.