Investigations into online inappropriate physician conduct will be up to the state boards. Online behavior from physicians and any other licensed health care professional should mimic their professional life offline. It's imperative that professional ethics is maintained online and offline.
The need for having an internal social policy is simple: it reduces risk. In reality, the social policy is most likely a variation on other internal, employee documents. One advantage it does have is that it clearly states what behavior is allowed and forbidden in specific social channels.