This is usually used for the individual or location that is responsible for sighing of the proofs.
Should be applied to users who are only to upload to the site, for example, a designer for pre-approval.
The site owner who is responsible for uploading the proofs as well as actioning the result.
Some key difference between Client levels and Administration levels are not immediately apparent, but Administration locations will have far more configuration options.
When creating Content for the various regions of your site you can also choose which level of user sees which blocks.
If any of the terminology does not fit with your workflow we can adjust this for Enterprise users.