Let's say you're in the chat window when visiting a scene. Then you switch to edit mode. Then you build and return to the scene. Chances are good that your chat window, still open, will now be open to a private message with somebody. You might want to chat something in public and accidentally send it to that person in private. They are bound to be in another scene than you at that point, so it won't make sense.
This can potentially be quite embarrassing. But it's surely annoying.