From a pure constructability standpoint, walls are never built "joining" to existing walls. They,for the most part, always just butt into them. So why does Revit always join a new and existing wall. It is very frustrating to have to constantly go in and "disallow joining" of new walls that connect to existing walls. This join causes issues both graphically and with functionality of the model.
My idea is that by default (as it could be changed) whenever a new wall is created, it only joins to walls of the same phase and if it butts into a wall of a previous phase the end is set to disallow joining.
You could take this a step further and make this an program wide option so those who thought it was a horrible thing, could turn it off (although I don't know why you ever would).
Another option would be to give us the option to turn off wall joining by use of the control button similar to turning off copy when mirroring. Then you could hold the control button down when you first click to start drawing a wall to control that end and/or the second click when you end the wall to control joining of the second end. That would be super awesome and extremely helpful and time saving. Man, that's such a great idea, I'm going to fantasize about it in my dreams tonight.