When you absolutely have to haul something back without support vehicles by blasting its supports first? But seriously, I have no idea.
It's not a winch, it's a harpoon gun waiting for CQB functionality when the Crab claws will be able to grip, rend and tear.
to winch it back up when it has fallen backwards in combat...(after repairs for example) i think there are a few more mechs with a winsh in front a locust has one too and i think a raven has one too...