[tomjen3]

Because otherwise you have a bunch of images and not a 3D object.

But this is far from the only thing people use it for. Basically it is used, or might be used, anywhere else you would use a cluster.

Here [http://www.youtube.com/watch?v=14ZSXCqOML0] is a real-time rendering of the Julia set (in 4D, so you are really watching the projection).