Little known fact: the Echo base on Hoth wasn’t terribly big. When the Millennium Falcon was there, all the fighters wouldn’t fit inside, a few had to be parked outside.
The rugged Y-wings were the only ones that could withstand the punishing cold Hoth nights. It would have been fine if they coud have been left running on nominal power to prevent them from going cold, but that would have made them easy to detect from orbit. They had to be shut down completely.
Once cold, even the Y-wings were very difficult to get up and running again. You had to bolt the rear panel open, install a heater and wait until the temperatures on the inertial dampers were on an acceptable level. If not, igniting the engines could throw the inertial dampers out of whack and the ship could read its own sensors wrong thinking it was on a free fall. As an emergency measure, the ship could then spontaneously shoot up several hundred kilometers to fix the fall – which didn’t exist. This could happen with or without the pilot.
It was a theory suggested by one of the engineers of the Echo base, the heating procedure was merely a precaution based on this theory.
But, you know, sometimes theories are verified empirically by testing. That particular Y-wing testbed was recovered much later. No pilot was on board the escaped Y-wing and the guy responsible for the heating was fired... only to be rehired. The rebels were a little short on personnel on Hoth.