Facebook has the right to use your picture in an advertisement. I find that disturbing. I'd imagine Barack Obama's account might have some useful images (they'd never do that, but it drives home my point).
They may never do that, but who else might? The agreement states that the rights are transferrable, may be sublicensed, etc., which I would imagine they would do in bulk. Plus, that content is now theirs forever...twenty years from now, fifty years from now, it could still be in use.