Can one assume the important bit, is getting the release signed... and as to before or after this will no doubt vary for a number of reasons;
The model may want to review shoot images particuarly on a tfp based shoot before signing off.
On a commercial shoot the photographer may want to protect against a waste of resources and hence will ask for the resease pre shoot.
Personally I believe you have to trust the person you are working with to do the right thing and that goes a lot farther than formal procedures. I have on ocasion forgotten to get a release signed and have never had a problem getting one on request.
I am sure there will always be exceptions or extreme cases, where someone will wind up saying if only "....." stuff happens but hopefully only in a small minority of cases.
Tony