The purpose of the SAT is to be a unbiased barometer; say what you will about it, but everyone takes the same test. Unfortunately, a 4.0 GPA from an obscure high school may tell you very little about a candidate.

I don't know how much admissions officers care about 96th versus 99th percentile, but if someone has an otherwise amazing resume yet ranks in the 40th percentile on their SAT, that's a bit of a red flag.