GL Viewport, multiple viewports, efficiency.

Hello gang. I tried using the GL viewport patch thinking that it could give me a different "camera" of my 3d scene without having to replicate the whole scene and split every parameter except ones that pertain to the view. I had a look at the example for gl viewport and it seems to just duplicate all the geometry etc anyway. what are the performance implications of this and/or how can I streamline it and have a setup where the scene (model loaders, lighting patches etc exists only once and I can observe the same scene from two places in 3d space? Does it make a difference either way?