Eh. You never know. People leave breadcrumbs of useful info in what they deem not useful. Further, things that you might not think twice about (ex: casually mentioning what car you drive, a coffee shop you went to that day) might reveal a lot of information (eg: your political leaning, rough geographic info etc). If you still have access to an old account, dig through your comments pretending to be a spy (or marketing agent) trying to learn as much about you as possible, with 0 prior knowledge - you might be surprised how much you learn.
Does no one remember the Ellen Pao era