Branches or Branch Groups?

There are 2 levels under Administration > System Configuration > Branches; being Branch Groups and Branches.

Members belong to a Branch. 

Branch Groups contain 1 or more branches and admin users are assigned a branch group - giving them access to all of the members in the branch(es) in that branch group.

This allows a mixture of users and branch access by assigning different branch groups to different users. In practice, there is typically a one-to-one relationship between branch groups and branches, but more complex arrangements are possible.

Click the Manage Branches button to add, modify or delete branches. Note a branch cannot be deleted if members are still assigned to it, if you want to delete a branch that is still in use, move all of the members from that branch first.

To assign branches to a  Branch Group, click the edit link under the branches column on the Administration> System Configuration> Branches page, you can then select the branch(es) to be included in this branch group, and the branch group will then appear in the drop-down list on Administration> System Configuration> User Administration so you can grant users access to the branches in that branch group.

Note those users with Admin permissions automatically get access to all branch groups, you need to uncheck the admin column to save the selected branch group.