There are a lot of short sections of track that go to something like a grain elevator. They are still worth minimal maintenance to keep operational, but you wouldn't build those tracks today or rebuild if something major happens. They often go more than a month without any trains, then other weeks where they have several. These sections are not worth upgrading to modern switches or computer controls, so you have a trained crew that section, but once the train hits the mainline the crew leaves to go home. Since this crew doesn't get much practice in the real world you need to give them training so that they haven't forgotten how to run a train when the next time comes.