WHAT IT REALLY MEANS.
You can schedule a 250ish mile cross country two weeks in advance, and the spoogebag who really owns the plane can just take it, while YOU are already pre flighting it.
It rarely happens, but it does, depending on the contract with the school.
I've been screwed a couple times, 30 minute ride to the airport, gassed the plane up, in the middle pre flight (once when it was 10 degrees out) and the guy says, I need to take my plane (guy didn't even do his own pre-flight, just checked the gas and got in and went.) The 2nd time was the last time I flew that plane in particular.