When designing a multi-site environment, here are the considerations you should take when deciding which sites require a Global Catalog:
- Use a Global Catalog instead of Universal Group Membership when AD information is required by an application at another site
- Uses more bandwidth compared to Universal Group Memberships
- Requires greater computer resources compared to Universal Group Memberships
- When you want to control Global Catalog replication, use the Preferred Bridgehead Server setting
- IgnoreGCFailures registry key; apply to all DC to prevent GC failures from preventing logon
