I haven't looked at everything yet but the thing I like best so far is being able to organize all my yarn! I wish I were at home so I could go through it and put it all in. It gives you projects for all the yarn you have.
I like the fact you can look up a yarn, and see all the projects that can be made with it. That's half my problem, I buy yarn just because I like it but have no idea what to do with it. For example, I looked up Noro Kureyon and there are 1,138 projects for it! If I even liked half of them well wow! For Lambs Pride Worsted there are 887 projects.
You can enter all the projects you are working on, and it enters the yarn details for you, as long as it is entered in their system already.
I just started looking around so I'm sure there is so much more to it but I think it's fun so far!