Scrubbing the slider when animating definitely helps in evaluating the motion as you go. Otherwise, you're stuck having to endlessly render the shot, evaluate, make changes, then re-render. Pain in the butt. Without a high-end video card designed for maximum polygon redraw, most 3D apps will lag in this area. Even Maya or 3dsmax. I'd consider investing in the 3dlabs Wildcat 4 for serious work, but then again, I don't know if it will work with Carrara.