You pull the barbell up from the ground (like a deadlift) while dropping into a squat, and then get it up over your head while standing up. It is much more explosive than either the deadlift or squat separately.
Why… well, it’s a sport where you compete to lift the most weight. The other competition lift is the clean and jerk.
For my old ass I do it because it’s so hard and the rest of my life is fairly soft. Waking up and getting beat down by some snatches (or occasionally having a great session) keeps me level headed in other areas of life, I guess.
If you’re not a competitive weightlifter but still training explosiveness for other sports then you’re better off doing variations on the lifts. Like hang snatches, power cleans, power snatches, etc.
Totally fair, all of it. Thanks for the explanation. When you put it as simply as “it’s about who can lift more weight,” my question looks dumb in retrospect, of course.
It would be just as easy for someone to incredulously ask me why I love BJJ, despite being hypermobile and having a much higher chance of injury as a result.
It’s about what you love. That’s why you do it. That makes perfect sense.
The point is to use the explosive power of your legs to optimally throw & catch a very heavy thing over your head. It’s not designed specifically to work any particular muscle but test your overall capability. That said it’s much, much harder on core & shoulder stability in particular than either deadlifts or back squat. Or front squat for that matter.
Oly lifts are humbling in that being able to squat or press a lot of weight doesn’t necessarily mean you’ll be able to snatch a lot of weight because there’s so much technique training required. The explosiveness and the sense of timing is very hard to learn.
To answer an aspect of your question that other commenters haven't addressed, the snatch works hip and shoulder mobility in a way that deadlifting and squats do not. The barbell is driven by the explosive hip hinge (unhinge?) directly up, so it is a departure from deadlift even if it looks like it would train the same muscles. Training your snatch lift in a non-competitive sense really exposes imbalances the lifter has. Your hesitance is really reasonable though, it's a non-trivial lift so coming into lifting completely new and trying to throw a snatch up isn't a very good idea.
But - it being explosive makes perfect sense, but what does it work that deadlift or squats alone don’t? Or is the point the explosiveness?
[0] https://youtu.be/UBc5N_-xdqo