If you buy 12 there is often a case which is a lot cheaper. I don't drink that much that it makes sense to stockpile; I also have the problem that if I have a fridge full of beer I am going to drink a lot more than I would otherwise.
I may be in a minority, but I prefer to buy a couple of beers just once in a while.
I buy a case at a time, but only put two or three at a time in my fridge ;)
Sometimes, but not often for the particular craft ales that these offers usually apply to.