I keep track of the books that I have in my "library" I love that I can click on a book and see the projects that others have made. I also look up patterns and yarn.
I prefer KH for questions and sharing and "social" posting
I also prefer KH when I need to learn something new or remember how to do something ... like short row with a wrap, yesterday ...
I think you could spend 8 hours a day on Ravelry and still not use every single thing on the site! It is a wonderful resource !!