lot of what a roto artist does is behind the scenes, so what you see in the final film does not really reflect their work. Much like a Compositor, their role is to help make each shot and all its components seamlessly fit together. They create mattes to help other artists build up a shot in different layers (either in front, alongside, or behind something in the live-action plate) and provide hold-outs that help other artists add shadows and reflections that match the plate.