Policies supercede Preferences
When it comes to Group Policy, a few policies and preferences overlap and allow you to configure the same setting for targeted users or computers. To resolve such situations, policies always have priority over preferences.
The above tip was excerpted from Mitch Tulloch's book Training Guide: Installing and Configuring Windows Server 2012 from Microsoft Press.
Mitch is a nine-time recipient of the Microsoft Most Valuable Professional (MVP) award and a widely recognized expert on Windows administration, deployment and virtualization. For more information see http://www.mtit.com.