There is basically "assigned seating" in regards to sleeping cars. Someone could book a Family Bedroom from MSP to FAR and thus block a family who wants to book from CHI to GPK. In the "olden days", 60's & 70's, before Hub-and-Spoke. airlines would fly one-plane "routes". I flew one plane; MSP -MKE-IND-ATL-MCO, with passengers getting on and off at each airport. Perhaps someone was blocked from a Minneapolis-Orlando flight by too many Milwaukee-Indy bookings. Similar situation, but the airlines handled it. Yes fewer stops and seats, but before today's massive IT/Computer Booking infrastructures.