It can hurt you at a job interview. While prospective employers may not be allowed to ask for your social media passwords in some states, they can still read your profile and make hiring decisions based on what you've posted. For example, post a bunch of drunken photos on your Facebook page and you could look like a hopeless frat boy to a potential employer.
Cyberbullying. Facebook is increasingly a playground for cyberbullies. Teens have been ridiculed and harassed on Facebook, sometimes leading to tragic results. In some cases involving adults, Facebook threats have even gotten people in trouble for witness intimidation.
It could provide clues to lead to your arrest. If you are on the lam, maintaining your Facebook account may not be the best idea. You could accidentally provide clues as to your location and police could presumably be check to see where you are logging on.
You could lose your court battle. Evidence from Facebook and other social media sites are increasingly popping up in lawsuits. Oftentimes, in divorce cases, one party will use Facebook evidence to prove that the other party is hiding assets, is an unfit parent, or is just unbalanced. Remember that what you post on the Internet has the potential to remain there forever.