The point is, you used to have to have a separate office. You had a desktop PC with a CRT, a bookshelf, a filing cabinet, a landline, a printer, boxes of software on CD-ROM, and so on. Remember how much room that took up?!
Now that everything's digital and on your phone/laptop, most people don't need any of that anymore. It's kind of crazy when you realize it. You don't need a dedicated room -- you can use whatever room in the house is currently quiet and unoccupied.
Decent ergonomics still require a dedicated space. Or else carting a lot of crap around to whichever room is quiet, then adjusting it to fit that space, assuming it's even possible without unreasonable amounts of effort.
Now that everything's digital and on your phone/laptop, most people don't need any of that anymore. It's kind of crazy when you realize it. You don't need a dedicated room -- you can use whatever room in the house is currently quiet and unoccupied.