X11. Imagine you have two floors and you want a pony wall to go from ground level to the middle of the second floor. Above that is non-pony wall.
If the walls in the plan view are aligned perfectly and you only put pony wall on second floor, you would have a pony wall sticking a few inches out over the first floor wall. The wall has to be smooth all the way up to the top of the pony wall.
If you're thinking"Well, just make your walls non aligned and put regular wall on first floor, I cannot because I'm following the 2D ACAD file the architect gave to me.
I hope you see my point.