VCL supports separating sets of users into organizational units using what are termed Affiliations. The idea is to allow multiple institutions to use a single installation of VCL but be able to manage things such as authentication separately.
Every user and user group has an assigned affiliation. There are 2 affiliations that exist by default - Local and Global. Local is to be used with the built in accounts that can have users created using the functionality in vcld --setup. Global is a special affiliation used for various configuration purposes. It is to be used for assigning default values to things when there is not a specific value configured for a given affiliation. The Global affiliation should not be used with users and user groups.
Authentication for each affiliation is configured in the conf.php configuration file.
Each affiliation can have its own theme configured to be displayed for users of that affiliation.
Various parameters such as how long before a reservation is timed out and content of emails sent to users can be configured per affiliation.
There are a few User Group Permissions that can be set to allow admins to manage things for their affiliation only such as User Lookup, Managing Block Allocations, and viewing the Dashboard. Also, most users can only view statistics on data related to reservations by users of their affiliation only.