Asteropê I'm not totally sure, but many people on GR use the star ratings to indicate a lot of things such as interest, disinterest, etc. Instead of putting it in a shelf titled "really-want-to-read" or "not-really-interested" they may give it 5-stars (or 1). When searching through your GR books that are added to your account/shelves, you can sort by star ratings. These 5-stars (or whatever they are) could then be used by people to sort of prioritize them. I personally do not do this. I only give stars to books I've read and I put books on shelves to help sort them. But I do know many on GR use the stars for various methods, that have nothing to do with whether they read the book or not. And as far as I know, there's nothing in GR rules that says you can't review or rate a book unless you've read it. I tend to rely on reviews over star-ratings, when I am interested in a book and am wanting to know if it's something to read or not.