The reason to take walls rather than destroy them :)

[Dorkus]

well, easier to sap and take the walls, imo.

you ahve to select one and only one unit to get up on to a wall. if you try to get a group up there, or if you select multiple units, the cursor grays out on the walls.

annoying when you want to send multiple infantry units up a wall. though in truth multiple units aren't that useful on walls in any event.