Likely so you could see things other people have open-sourced that you might not have before. It would probably be most useful for getting ideas of what people have made rather than finding projects to contribute to, since a lot of these will be abandoned projects. (Or you could see where people contribute their time) I think seeing profiles of "active" users might be more helpful.
I can see the appeal of novel approaches to the discovery problem. I sure wish apple had this for the app store! Anyway, it's fun, and the internet can be boring when it's too rigid, so that's why I'm using it. This extension reminds me of /r/all