If you have a HQ and multiple branches you might consider configuring a DC in each site as a GC (Global Catalogue) Server to improve AD performance in the branch office site. A local GC is not your only option though. You could consider configuring a local DC to use UGMC (Universal Group Membership Caching). GC's and UGMC's both have advantages and disadvantages, here they are:
AdvantagesUniversal Group Membership Caching
Faster user logon
Faster AD queries
Support for a local Exchange Server
Increased AD replication traffic
AdvantagesImportant Note: UGMC is enabled at the site level.
Less replication traffic (compared to GC)
Less WAN traffic
No support for local Exchange Server
No advantage if Universal Group memberships change often
To provide fault tolerance, a mixture of UGMC and GCs can be used. For example you might place multiple GCs at head office and enable UGMC at the branch offices. This will provide fault tolerance for WAN links and individual Domain Controllers.