I don't see much benefit from LinkedIn for my career, since I don't want to change jobs and my contact list is largely driven by whichever project I'm working on. But like Facebook it can be interesting to keep in contact with former work or school colleagues, people you may not wish to be Facebook friends with. So, for me anyhow, LinkedIn is a second circle of Facebook, if you will. People I know through work but whom I don't know all that well socially, and don't necessarily want to. But used in that context it's mostly voyeurism, frankly, as the social interaction on LinkedIn is corporate nause, rather than pictures of peoples' families or tales of their travels etc, a mutual sharing of life experiences with people you like.
If you don't care about keeping up with such people, and don't need to expand your business contact network or find a better / different job, I'm not sure there is an advantage.