Relatively speaking, private bedrooms--or even bedrooms--are a modern invention. A house might have only one room or just a few, none of which could be set aside for sleeping.
So if an amorous couple desired, uh, privacy, then they needed a box bed. Amusing Planet describes the other purposes of the box bed:
Aside from privacy, the small enclosed space of the box bed trapped body heat keeping the sleeping person warm during winter. It’s also possible that the beds offered some degree of protection against intruders, especially wolves and other animals, that might have entered the house. It has been suggested that peasants kept their children inside box beds while they went to work in the fields.
In Europe, box beds continued to be common until the Nineteenth Century, when the practice declined for hygienic purposes.
Photo: Wolfgang Sauber