Way back when South Eastern still ran slam door trains and I commuted to London, I tended to travel at the front of a twelve carriage train (because it was less crowded there), and thus had to walk back along most of the platform at my destination.
On most days I (or other passengers) would need to push at least one door closed as it had been left ajar, or partially latched by other passengers.
During daylight hours this generally allowed the train to depart as it saved a porter (remember those) from having to make his way down the platform.
At night, when the porters could not always see the open doors, it sometimes meant giving the door a kick whilst the train was accelerating from the station.
I read a story about a member of BR staff who didn't manage to close the door of an InterCity train properly and the door ended up being ripped off the train when it entered a tunnel. Said door was delivered back to her depot wrapped up in something, but I can't remember what.