[Stiglr]

Quick example for you: you're outfitting an aircraft for a flight sim.

You need to define the "ray" that describes the hinge point for ailerons, rudders and elevators, as well as flaps... and you need to animate the stick, rudder pedals and all the moving dials and switches in the cockpit. And, more complex, you might have a fairly complicated animation for how the landing gear goes up into the wings/fuselage, and the little bay doors that go with it.

These features allow you to set up the meshes, program in the ranges of motion and to preview the animations, while you're still in AC3D; so you can be more confident that the affected bits will animate properly once the aircraft is imported into a game or simulation engine.