As a parent of college aged children, I've stressed the importance to them about being discreet and cautious about content and photos they post on social media. Employers nowadays tend to checkout more than your LinkedIn profile so it's a good rule of thumb to never post anything you wouldn't want a boss or prospective employer to see.
Overall, social media is a very grey area when it comes to mixing your personal and professional life. Technically there aren’t any rules, but where common sense is the general rule, mistakes are easily made and messages on these platforms can be easily misinterpreted. If in doubt, don’t post it!