We used this in a videogame engine test framework to verify specific game states against gold-master images. It was particularly useful for verifying when our physics engine had changed in subtle ways; one of our tests involved dropping a couple of boxes on top of each other and verifying where they landed.

All kinds of stuff would disrupt that test---which made it great for knowing when we'd changed something subtle that would have real impact on our game engine's users.

like a value of 15.000002 instead of 15.000013 but errors may accumulate in the end.