That is the part that I do not understand. Why would you want to maintain the brake pressure? If you were leaving the train for any length of time, wouldn't you want to release the air pressure and set the brakes on all the cars, thereby preventing the train from moving?
What am I missing here?
Yes, I've found online operation manuals for other train departments that say just that.
What am I missing here?
Incompetence, lazy, cutting corners and saving time, leaving without following procedures, etc...
What are you missing? The same thing I’m missing.
I should clarify. Trains are not like trucks trailers with spring close brakes. They use air pressure both to open and close brakes. Each car has air reserve tanks so that in a supply line brake, the brakes are applied. But that reserve tank is not going to last forever. It is intended to give time for an operator to come set the hand brake, make repairs, etc.