Forget about the snap sound. It's a kids' thing IMO. It was cool for a week or two when I bought my first real gi at 19. Then I realized it was just for show.
My understanding is that the sound is caused by the fabric accelerating and whipping through the air, so the sound demonstrates that your technique has some force (mass * acceleration) to it. Which admittedly, is not that impressive for someone whose not a beginner, but I think for beginners it can be helpful way for them to judge their own technique.