Google is your friend
My boat racing knowledge is very poor but it seems back in the day with under-developed and researched sails that wet sails in a strong wind was advantageous. Despite the boat being weighed down cotton fibres expanded when wet and held the wind better. Just from my googling - could well be wrong but theres a start.
It's always used by a backmarker coming over the top as well. Just wouldn't have the same ring to it with a leader kicking on the turn.