There are a few places in ServiceNow that some default Reference Qualifiers are often needed. For example, in the Incident Table, you can add a Reference Qualifier to restrict the Caller ID field to only show Active Callers. These are not setup OOB due to varying customer needs.

What is a Reference Qualifier?

"Reference qualifiers are used to restrict the data that is selectable for a reference field, using either the auto complete support or the magnifying glass lookup icon. The reference qualifier may either be a static encoded query string or JavaScript code that returns an encoded query string. Reference qualifiers are defined in the Reference qual field on the dictionary record for a reference field"

"There are several out-of-box examples of standard reference qualifiers. To view them, navigate to the System Definition > Dictionary, and then filter on records where Reference qual is not empty. "

http://wiki.servicenow.com/index.php?title=Reference_Qualifiers

"Active User" Reference Qualifier Examples

Table: Incident [incident]
Column: caller_id
Reference Qualifier: active=true
Table: Task [task]
Column: assigned_to
Reference Qualifier: active=true^roles=itil
Table: Change Request [change_request]
Column: requested_by
Reference Qualifier: active=true
Table: Request [sc_request]
Column: requested_for
Reference Qualifier: active=true
Table: Variables
Column: Any Variable that is a Reference of the User Table
Reference Qualifier: active=true