Raytrace map provides fully raytraced reflections and refractions. The reflections and refractions it generates are more accurate than those produced by the reflect/refract . Rendering raytraced objects is slower than using Reflect/Refract. On the other hand, Raytrace is optimized for rendering 3ds Max Design scenes, and you can further optimize it for your scene by excluding specific objects or effects from raytracing.
Thin Wall Refraction simulates the "jog," or offset effect, you find when you view part of an image through a plate of glass. For objects that model glass, such as a Box in the shape of a window pane, this map is faster, uses less memory, and provides a much better visual effect than the Reflect/Refract map.