One part of the rendering process is to determine what pieces of the game can be given to the computer, that only the computer renders. In many situations, the people in the animation studio will work until such and such a time in the day. Then they all stop and the computer animation takes over. The computers render all of the tweens between this scene and that scene. So you might have spent a lot of time drawing the first 15 minutes of the movie, and not have drawn a significant amount of frames. This is because the computer can generate a lot of action on a frame-by-frame basis.
There are 3 basic task lists that a studio can use to drive the rendering process.