LinkedIn has been described by many as Facebook for business, but it's fair to say that's not fully accurate. Besides a way to express personality, connect with others, and show career history and highlights, it's also an opportunity to showcase one's professional possibility and to make a unique business contribution through valued content.
The key difference, obviously, is that the idea is to be PROFESSIONAL about all of it, including being truthful, earnest, and respectful. Facebook, much as I do appreciate it, is not any of these things for a noticeable chunk of users.