Active Directory sites are the easiest way of defining ConfigMgr site boundaries, because they are based on physical segments. BUT besides that, you have to keep in mind that they are also static in two different ways:
- All the different subnets have to be manually included and configured in the Active Directory sites.
- Once an Active Directory Site Name is selected as an ConfigMgr Site Boundary, ConfigMgr will check on the selected Site Name. Even when you rename the Active Directory site!
For more information about site boundaries: http://technet.microsoft.com/en-us/library/bb633084.aspx