The smooth tool is best for making smoother paths on slopes. I think they need a stronger smooth option, it feels a bit weak. It would also be great if there was some kind of path snapping to terrain so you could raise/lower a path and the terrain would snap to it.
With smooth cliff edges like previous games, we sadly don't have that anymore. To get a similar effect though use, "Flatten to Surface", that allows you to flatten the side to get a proper cliff,