When I visited
Fallingwater the docents talked about the versatility of the furniture and how when the Kaufmanns had large parties FLW designed chairs to move to the dining area and after dinner back to the lounge. Maybe he only approved if he chose it!
Also, I live fairly close to his
Pope-Leighey house and the furniture that you can see in the link you're invited to sit on for the docent's big number. It's pretty comfortable-doesn't beat a modern couch but is as good as anything else from the '40s.