Why am I on linkedin?

I was filling out a form to join a blogging network and one of the required pieces of info was my linkedin profile.  When I went over to Linkedin, which I hardly ever do, I realized I have been on there since 2007.

Do you know what that means?  Five years of not knowing what the point of being on Linkedin. Are you Linkedin?  If so can you please tell me what I am supposed to do on there?  Why am I there? Anyone know?

A while back I went on to my profile and on the right hand side it said "link your resume to complete your profile." So I did, and guess what, apparently that is a generic message because all of a sudden my profile had all my career info listed 3 times. Even then my profile sits at 90% complete.

Linkedin also keeps telling me to add another email address to my profile. I refuse. Why does it keep asking?  Facebook doesn't bug me for multiple email addresses. 

How about you?  On Linkedin?  Profile Complete?