It depends on the process. In some schools, they send the materials out to a prof for review, and they rate them on a scale of 1-5, in which 3 means good enough. Obviously you don't want to get a 1 or 2, as that can hurt. Other schools, an admissions officer looks at the materials, so you just don't want to stink.

Is your DC submitting any supplemental materials- music , art , science research? Thoughts on whether this helps or hurts you in the admissions process?