Lightwave will render out the scene from the point of view of the currently selected camera. However, if you've go (for instance) a scene with an animated camera that you've now got set just the way you like it, and now need to render a portion of the same scene from a different point of view, well rather than move the single camera and screw up your painstaking motion, you can simply insert another camera and render from that point of view.
Another alternative is to have multiple cameras with different resolutions and scene settings for specific results.
Really, there's probably a whole bunch of other reasons for wanting multiple cameras that I've not even thought of here - it's simply a question of what you want to use them for - or don't if you don't have a use for it...
