Google Message Security for Google Apps Administration Guide - Manual (Page 119)

Administrators 119
User Administrators
A user administrator manages the general user administration tasks such as
moving and suspending users.
Note: This administrator does not manage the Default User or the Message
Center’s user-access settings. These are managed by the organization policy
administrator.
Positioning User Administrator Authority Records
User administrators are generally assigned to strategic organizations that contain
users. In the following example, the Big User Org user administrator has different
suspend, reset, and user-management policies from the other User Orgs
managed by other user administrators.