A Microsoft SharePoint admin must pre-approve a Microsoft SharePoint user to access SigningHub. This pre-approval maps the Microsoft SharePoint user as an Enterprise User account inside SigningHub. However, only a certain number of SharePoint users can be approved, as limited by the subscribed service plan of SigningHub.
The "SigningHub User Access " section is used to allow the SharePoint users to access the SigningHub enterprise account. In this regard, the SharePoint admin can add/ remove users from the SharePoint users list. The Active Directory users of SharePoint can also be added. If a user being added is already registered in SigningHub, they will be activated, otherwise an invitation email will be sent to them to create a SigningHub account.
In case of removing any activated user from the users list, the user's account will be blocked and they will not be able to access the SigningHub add-in from SharePoint.