You can deploy Exchange Server 2007 directly into your organization’s existing Active Directory topology. For many organizations, deploying directly into the existing Active Directory topology greatly simplifies the overall management of the Exchange 2007 deployment. However, given the extensive access to domain controllers and global catalog servers that is required by Exchange 2007, you may decide to create dedicated sites for your organization. You might want a dedicated site if other applications in your organization must access Active Directory domain controllers and the global catalog server.