I don’t know if these even exist anymore, but I’m imagining a class that meets in a room of workstations. Students can login to any workstation in the room. In this kind of shared environment, you may not want to have a student start a screen session and use the resources of a workstation when they logout. They could be sucking up cpu time from the next person to log in (from the next class).
It’s a scenario that might make sense here. But then again, having a watchdog script just kill leftover processes has been doing this same job for forever. Including this use case in systemd seems like overreach.