The only way to screw something up is if you don't like the effect. Some material can begin to look unreal the more reflective they get but go with what you like. Overdoing specularity and reflection can have an adverse effect on your render time though, so when you are rendering your scene I suggect using the TIR option in the Render Options dialog. This way you can limit the number of "Total Internal Reflections" and keep the raytracer from bogging down in infinite reflective loops.