What ?
Why ?
Walls that connect to adjacent cliffs would look prettier. They would also indicate better, whether there is an actual hole between the wall and the cliff.Walkable space that can't be closed with a wall are surprising for the user in a bad way and inconsistent with general behaviour of walls.
Tile-sized non-walkable space wich looks like it should be walkable (and accept walls) also surpises the user in a bad way and looks ugly if the end point of a wall.