The high hang snatch can be used for a number of different reasons, however it is most commonly used to teach beginners how to properly pull underneath the barbell.
The decreased pulling distance makes the lift much more simple than when snatching from the floor.
In general, less moving parts makes it easier to focus on the details and not be overwhelmed with complexity.
As a training exercise, the common purpose is to develop better speed and acceleration at the point of extension, as well as increasing quickness when pulling under the barbell.
Another common way to train the high hang snatch is with significantly lighter weights, on active recovery training days.
The high hang position requires less overall movement, thus creating less demand and fatigue on your system.
High hang snatch reps are typically kept between 1-3 per reps per set and when being used for technical purposes, its best to use a weight around 75% of your max snatch.
But as always, the training prescription will come down to the needs of the individual that it’s being prescribed for.
In general, a good guideline to stay close to is: 70%-80%.