Tak 3k of dirt and move it somwhere then put it on the ground in one place tell me what you got...a quite big pile of dirt I suppose.
Now imagine a siege during Jh when enemy moves 10 wagons of dirt towards your walls and in 2 minutes you have a big mountain next to your walls.
The action would have to take around the time of harnessing but would still allow you to devastate someones hours of digging and flattening in a matter of minutes.