It would be useful in making a block in the style of mario that would move up once hit and make an item fall out. Exactly like Madsters Avatar does. If I wanted to make a one of those blocks, I would make a sprite that had an animation that moves its hotspot up once hit, but I don't want to move the collision masks hotspot along with the sprite because that would cause some freaky collision glitch between mario and block if they overlap. It's useful because its convenient and because I don't want to have to make a whole other sprite just for collisions.
I think you could do that with animation frames. I'll try to draw an illustration below:
|_| 32x32 box with hotspot at 16,16
|_| 32x32 box on top with 32x32 (overall image=32x64) empty space below it and hotspot at 16,48
That should work. You can do all the animations in the middle (you'd want like 1 or 2), but you just have to remember that the hotspot must remain the same distance from the BOTTOM of the sprite.