I'm using nonces as WordPress uses them. It's an extra security measure, a hash that is being sent to the server that changes within ever few hours.
If that hash is not there, the request is invalidated.
The page I am working on has many AJAX calls (about 20 or so). Right now, I have a difference unique nonce for each one. Is that necessary? Should I just keep it with one generic "AJAX" nonce used for all the requests?