I am quit aware how their functions works. But the hold postion functions stops the skirmishers from chasing the fleeing units. I also think that the function is really nice if you just want to poke a unit from the side or the flank. The problem with artillary is, that the skirmishers mostly run away when they a targeted by the unit they are shooting at. But especially in this situations, you dont want them to run. My main goal is allways to make the artiallry unit rout und then kill it.