It really depends what you mean. I assume you are talking about Multiplayer object (WebRTC channels). Well designed real-time multiplayer game is the game where peer/client cannot cheat. It means that any action which has an impact on the game and the "fairplay" should go through the host and he is the one to say if this move is correct/allowed or not.
But obviously there are some action which does not affect overall gameplay, for instance when player goes to the menu and change some setting (sound volume - that is trivial, but you know what I mean) then there is absolutely no point to inform host or other players about that.
Basicaly when you write multiplayer game it's you (the designer/developer) who decides which data gonna be sinchronized and which won't. Multiplayer object just gives you great tools to do it.