When you define a user segment, you are defining a target audience. ATG Self Service uses User Segments to:
Set field security on global fields. Refer to the ATG Service Installation and Configuration Guide for information on configuring security on global fields
Set list value security on list field values. Refer to the ATG Service Installation and Configuration Guide for information on configuring security on list values
Set value security on the intrinsic fields Owning Group, Internal Audience, and External Audience. Refer to the ATG Service Installation and Configuration Guide for information on configuring security on intrinsic fields
Identify targeted content displayed on Self Service sites
For information on creating user segments, refer to the ATG Business Control Center Administration and Development Guide.