If you have sites separated by slow or unreliable WAN links, the practice is to place a GC server at each local site, but this can increase the replication traffic. If the domain is operating at the Windows Server 2003 functional level, we can deploy domain controllers, which can store universal group membership information locally.
Universal Group Membership Caching is most practical for smaller branch offices with low capacity servers, which cannot handle additional load of hosting a GC, or locations that have extremely slow WAN connections.
When a user attempts to log on for the first time, the Domain Controller obtains the universal group membership for that user from a Global Catalog. This information is cached on the Domain Controller for that site indefinitely and is periodically refreshed in every 8 hours. Up to 500 universal group memberships can be updated at once.
The benefits of Universal Group Membership Caching are
• Faster logon times.
• Hardware upgradation to support Global Catalog is not required
• Low network bandwidth consumption.