For starters, it’s important to realize that court cases have accessed data from computers, smart phones, messages, videos, and more. The courts haven’t established a clear line of precedent in order to help law enforcement either.
But law enforcement has requested everything from photographs to medical records through the process of discovery. Discovery is when law enforcement tries to gather information related to a trial to help support their client. What you post on social media may, in fact, be relevant and requested if it’s related to a case.