It is irrelevant if everyone uses the same scale. When they don't, it can have some effects when comparing students coming from different scales if the scale information isn't asked for.
BTW ... here at A&M, there is no +/- ... only A, B, C, D, and F.
All I know is that this question was asked of the admission people in almost every session we attended during the campus tours we took and they all talked about using this profile that every HS completes...again they use this to level the playing field.
The bottom line is that they told us that they were looking for students that had challenged themselves (taken the advanced courses and not just the bare minimum), had success (got good grades...As and Bs), and were "involved" in some form or fashion.
Another interesting thing is that most of the schools downplayed the standardized tests (ACT and SAT). In fact, some schools no longer require them (Wake Forest for example...it is optional to submit a standardized test score). I think these schools are starting to realize that kids are taking all kinds of courses to learn "how to take the test" and are taking the standardized tests multiple times (5, 6, 7, 8 times) in order to try to catch lightning in a bottle one Saturday morning...ultimately they are finding these tests are becoming a less accurate predictor of success at college.