My uncle has one of these on his farm.
http://en.wikipedia.org/wiki/Pig_scalder
They slaughter pigs and then using the bucket of a tractor, raise the carcass and dunk it in the hot water. Can't be boiling because that would begin to cook the sub-dermal fat. I think the optimal temp is around 180 or so. Immerse pig for few minutes and then the fur/hair can be scraped off the pig with a knife (like shaving with a straight edge). They dont just skin hogs because the skin can be eaten and it is a source of fat. So when you keep the skin, you need to find a way to de-hair it and scalding is the answer.
My GF comes from a Romainian family and they have a different de-hairing technique. After the pig was stunned and bled out, they would drag the pig on top of a small pile of hay and then place more hay around him. The hay is lit on fire. Hay burns quickly, goes out quickly and wont seriously damage the pig meat. But it delivers enough heat energy to sing the hair off of the carcass.
I believe hot water has the same effect on chickens (I've never slaughtered a chicken before) and helps remove the feathers during the slaughter process.