One of the difficult things about high school is figuring out which people to be friends with. After all, it can make a big difference in your life! Being friends with popular kids is a good way to become more more popular yourself. Plus, your teachers might treat you better, you'll get more cool stuff (from being friends with the popular kids, who are also often the richer ones), etc. In the status quo, however, freshmen often enter high school without a very clear idea of who the popular kids are, so they're aiming their friendship aspirations pretty haphazardly.
But here's an idea for an enterprising popular kid to provide an invaluable service to everybody. He gets a group of his friends together, and they rate everybody in the school (or at least everyone they think is at least minimally popular) for popularity. Then he can make the results known to the whole school, free of charge! Now everyone worth thinking about trying to be friends with comes along with a numerical popularity rating. Sure, everybody's going to try to be friends with that one girl who was already a 4.8, and she doesn't have the time or energy to be friends with everyone, but since she's the most popular, it makes sense for her to be able to be the most selective about choosing her friends. And aren't the best candidates for friends the ones who deserve to have access to the most popular kid's friendship?
Now I'm the first to admit this system won't be perfect. The popular kids are likely to get ever more popular, since everyone will know that they're the people to try to be friends with. And of course everyone will have some incentive to be friends with that one kid who started the rating system, and with the raters that make up his circle of friends. (The latter can be mitigated somewhat if that first kid occasionally makes changes to the roster of kids who do the ratings.) So yeah, maybe there are better possible systems. But in the status quo, people are just trying to guess who's most popular by asking a couple of people or -- even more unfairly -- by judging by superficial cues like race and attractiveness and athletic ability. How is that fair.