Ah, I couldn't see a vid for it, either, but they say:
Sometimes used synonymously with snatch balance, the drop snatch is actually slightly different. While in the snatch balance, the athlete uses a dip and drive of the legs to unload the bar momentarily before driving under it, in the drop snatch, the athlete must drive under the bar with no upward push at all. This greatly limits the loads that can be used in the exercise, and as a consequence, limits its utility. It's more appropriate as part of a warm-up or to be used while progressing up toward heavier snatch balances.
Ok. I guess... I think it might be useful for learning speed under the bar. If you dip-drive it then you have more time to get yourself under it. If you don't dip-drive it then you will have to be faster. If heavier weights don't fall any faster than lighter weights then I'm not sure why one would be limited to light weights on this exercise.
It seems to me that all of those variants involved a slower drop under the bar than what the dude managed in the vid I posted. (I really hope you don't mind my posting your vid here random dude!) He also simply drops into the bottom position rather than needing to wiggle around a little to find the bottom of his squat.
I think I'm learning very slowly. I don't mind that given my aims etc. I guess I'm more attracted to drop snatches than the other variants.