If user does not want to get notifications from previously subscribed room then he must unsubscribe the room. Leaving the room will take him out of the room and he can not be able to send any request to that room. But if he is still subscribed to that room then he will be acting as an observer to that room, i.e. he will be getting notifications of all the public events of the room such user leaves or joins the room, chat broadcasted to the room etc.
So, if you are leaving room without unsubscribing it and joining as well as subscribing another room then you will be getting notifications from both the rooms.
Let me know if you have any further queries.