Using the legs to drive the bar allows the hips and back to...
Using the legs to drive the bar allows the hips and back to extend naturally while holding position throughout the movement. By not using the back to extend heavily against the bar, this preserves the posterior chain allowing it to continue to serve it’s prime function of control and stabilization of the barbell.
Here is Lester Ho (@lesterhokw) exhibiting snappy timing in his hang snatch. This is a great position to work from to practice timing and feel of using the legs.