They did this in first year and the year before my first year in my uni because there wasn't enough halls accommodation. I didn't have a bunk room but I know people that did, it's a good way to save money if you have a choice about getting one!
Also I think it depends on the room, some were twin rooms and had two of everything - wardrobe, desk etc, but the bunk rooms just had bunk beds in an ordinary single room, like my housemate's room next door now used to be a bunk room. The uni were just like 'people can go to the library to use a desk'. That's not enough space for two people.