Try opening the doors in a unibody car with it on jack stands.
The engine, radiator, battery and suspension weigh a lot. The front frame rails are designed to resist compression, not extension. When the car is bare, that is 900 or more pounds NOT pulling down on the cantilevered frame rails.
My 70 Charger has no rust anywhere and has never been wrecked but the body gaps did change with it on a 2 post lift. Not a dramatic change but it was enough to cause the doors to drag a bit when opening and closing.