Vanishing point

It really only takes up a lot of power when rendering, and that's one of the things I love best about the program; it has a preview window in the top left hand corner of the screen, and the manipulation area in the center of the screen shows everything you've made in wire frame, so no lag or loading times when you twist your camera for a better angle unless you've got a LOT going on. Of course, there are settings for that kind of thing, like how detailed your wire frames look before rendering, how good the quality of the render is...