Being lowered off the top of a cliff.
I posted some pictures of one of the course I was working on last week, and someone asked why in one of the pictures the rope had been clipped through a carabiner behind the belay plate. It was to add additional friction when lowering people off the top of a cliff or pitch. It makes a real difference to the control that you feel when lowering someone, you just have to remember to remove it and belay normally when the person is climbing up. It also means that the rope is locked off by holding it forwards rather than backwards.
Belay plate set up for belaying from the top of a pitch/crag, with an extra carabiner with the rope clipped through to add extra friction
The extra carabiner in action, whilst the belayer looks like he has locked the rope of incorrectly, the extra carabiner means that the rope is locked off by pulling it forwards, not backwards like when the belay plate is used normally on its own.