Why do we love to rank things?

I've been thinking of this because I've been writing a fair number of reviews on Goodreads lately. And it's gotten harder and harder for me to figure out how many stars to give books that I like. Three stars? four? What's the difference? Is a three star book really worse than a four star one, and do I have to choose? Often, I'd be happier to just write a review without having to assign a number of stars to a book. It just seems so - arbitrary. 



I first ran into this problem when reviewing a Star Trek novel I really like. It's obvious that comparing a book like this to an original SF novel is, in some ways, like comparing oranges and bananas. They're both tropical fruits, yes, but an excellent orange is a very different thing from an excellent banana. And some people just don't like bananas. 

The more I review, the less I like having to assign a star value to books. And yet, like everyone else, I like top ten lists, and even seek them out. Why do we do this? Why do we insist on ranking things, and, when it comes to books or other works of art, is there any way these star ratings are helpful? What do you think?