What is the difference between Global and Local Authentication type ?

We have configured LDAP Authentication in our environment and we are providing access to the users by using their LDAP Account user Id and we also assign the roles and Accounts/Groups to access the documents basing on the user requirement.

Basically authentication is happening at LDAP level and Authorization is happening at content server.

We create the users with global authentication type, One day we have received a request from the business user to provide admin access to his account.

We have configured this user with access type as global initially, later on we have received a concern from the user saying that, as an admin, why he, himself is not able to add more groups/accounts to his user Id.