This is to allow the appearance and comfort of conventional upholstered furniture while avoiding the usual eventual concomitant dinginess by allowing the upholstery to be removed for washing, without the intervention of a skilled upholsterer.
The (usually) timber frame is made to incorporate simple
mechanical devices that allow it to contract or partly collapse within its upholstery, perhaps by turning a crank hidden in or under the piece of furniture. After undoing a small number of attachment points the now-loose upholstery may simply be lifted off the piece as if it had been a loose cover of rather generous cut.
After washing, the upholstery is draped over the frame, and the attachment points lined up and tightened. As the crank is turned (or whatever) the formless pile of cloth slowly turns into a piece of furniture, as the frame expands and stretches the upholstery into place. The mechanism locks at the extent of its travel, thus preventing over-stretching.
Instead of stretching cloth and stuffing in panels over a rigid frame, the frame is expanded within a complete assembly of cloth and stuffing. As the pattern for the latter may be deduced from an existing example this method makes it much easier to change the upholstery material to a different sort.
Furniture of this kind may even be sold as a frame and a pattern for upholstery to be made by the buyer, or for that matter a set of measured drawings in lieu of a frame.