Which can cause a massive problem. No one knows what the future holds for them and there may come a time in someone's life when what they put in the public domain comes back to haunt them. A social worker I know became the butt of considerable media interest after a case she was involved in resulted in a tragedy for which she was initially blamed but later cleared. She had to frantically delete all the photos of herself and her family from her FB account and contact everyone she knew asking them to do the same with pictures she'd sent before the press got them.
In the US it is considered "due diligence" to ask for the candidate's facebook log in details and to assess the content.
One candidate lost a senior management post because of photos of a night out, and several people have been sacked for the content of their facebook sites