These chairs that fit in the wall

I was just thinking of a teenager, making minimum wage, putting one back, dripping with mustard,ketchup,mayo, ice cream,ect.

It depends on wether you designed the room with that space or not. For instance if it is a wall for a room towards the inside of the house (not an outside wall) and you simply used less insulation in those spots and routed conduit around the shelves- you would lose no floor space- and if you planned to have say a 300sq/ft room and there were 300sq/ft of floor when done... well- no space lost. But mathematically we can crunch the numbers and determine that useable floor space might actually increase as well as utility through this design. One must remember that cubic space is lost- but most people don’t use the upper half or even 2/3rds of a wall for anything functional... unless they put a shelf there- in which case would you also argue one shouldn’t have kitchen cabinets or book shelves or entertainment centers for a tv?