I don't know - presumably for the liver and kidneys to flush out all the toxins. Apparently, the liver can go downhill for a long time without showing problems, but when it does then it's too late.
Anyway, I'm on the gin right now.
At least he kept off the hard stuff! Currently reading about Warren Zevon, who was doing several bottles of vodka a day. No, I don't know how it's humanly possible, but I guess the body adapts. How do you hide it though?