The user lists are named sets of E-Business Suite (EBS) Users.  You can use the lists in Application Auditor (AA) to make audits more selective, and to filter audited transactions.  In Segregation of Duties Violation Manager (SoD VM) you can use the lists to limit the scope of the access violation snapshot.

In AA, they let you take a closer look at what a set of users do, while ignoring the rest.  You can also reverse the logic, and ignore what a few users do, but audit what all the other users do.

In both cases you are refining the selection criteria for when AA will respond to an audit event.  Thus your controls are more targeted and exception-based.

In ProView for Application Auditor, you can use user lists to filter audited transactions.  This is a reporting convenience, and it is dependent on the users in the set at reporting time.  The filter can include or exclude the users on the list.

In SoD VM, you can create a snapshot of user access violations for the users on a user list.  For example, you might want to see the violations for several of the accounting staff.