It lets you create sightlines anywhere at the cost of damage.
Useful, i guess?
Teammate 1: "Yo, can you skeleton key this here wall? It will make a great sightline.'
Teammate 2: "Yeah sure!"
*BANG BANG*
Teammate 2: "Home improved."
Based on the Kate Hudson movie Skeleton Key, in which an old lady steals her youth, skeleton keying is when you and your friend are both deservedly hungover, and suddenly one friend begins to feel much better, and the other friend much worse. The friend that is feeling better is 'skeleton keying' the other, or stealing their essence.
Alex, a minute ago I was fine, now I can't get off of the floor, and you're suggesting we walk to McDonalds? How are you feeling better, are you skeleton keying me?