A Barber Hauler is not a crazy man with scissors but rather a line that allows you to adjust the clew of a sail to optimise its trim.
with an Asymmetric spinnaker you can only go so far up wind before it will lose all its trim and start to collapse but this is mostly because there is not tension on the leech of the sail (the back edge).
By attaching a line to the clew and pulling the clew down and forward, onto a cleat, you can increase the tension on the leech, effectively straightening the leech just enough.
Combined with a tight luff (leading edge of the sail) you can point considerably higher before your Asymmetric becomes less useful.