Well, it depends upon what you're trying to achieve .... If you're not using raytraced reflections and refraction, or raytraced shadows, there's little point in having raytracing enabled. Likewise for displacement. Smooth Polygons can help make low-poly objects look rounder and less angular, but it doesn't always work properly on everything, so it's best to leave it off unless you specifically need it. Remove Backfacing Polygons is an option provided to increase render speed (and to fix certain render quirks), but any performance gain is minimal, and the backface culling usually causes more problems than it fixes, especially with wings, hair, etc. Texture filtering eats up system resources, although it can produce nicer results with some textures. Most people leave it off, because it seems to make some textures too soft.