Because you can render from any of the cameras you have. This is useful to get shots of the same scene from different angles, and lots of other stuff. You can use the face camera to get a head shot, then use the main camera to get a full figure shot, then use the dolly camera to get a panoramic shot - each one with their own settings. Say you were doing a scene of two people talking and you wanted to get 3/4 face shots of the person who's doing the talking at the time. You could move the main camera every time you switch to view the person talking, or you could set up two cameras, one for each shot and simply switch back and forth between the cameras to change what you see. Stuff like that - less work for you. The renderer will use whatever camera you currently have selected. So if you're viewing with the Aux Camera when you hit render, then that's the camera that will be used to create the render. Hope this helps, Unzipped