Depends upon what you want to work on.
Low hang - below knee
Mid hang - about knee
high hang - above knee
high hang to work on third pull. Mid hang to work on top of 1st pull, 2nd pull and third pull. Low hang work on mid point of first pull, 2nd and 3rd pulls.
If that doesn't make sense, please tell me and I'll explain in better detail. But for clarification 1st pull is from floor to the knees have scooped under the bar. 2nd pull is from the end of 1st pull to full extension - some call it triple extension - you've driven your heels through the floor, you've stood up violently, your hips are to the bar, and you've shrugged as violently as possible trying to get the bar as high as you can with your arms staight. 3rd pull is getting your arse under the bar and receiving it.
I may be a little off in describing the first pull. And if I am that's my own novice interpretation.
I've always seen hang or box movements as a good way to learn to be as violent as possible with the 2nd pull.
All the best,
Lifting heavy stuff is fun and relative......