The second GPO that exists by default in even a fresh installation of Group Policy is the Default Domain Controllers (DCs) Policy. As the name implies, this policy is for your DC servers, and taking a look at the policy itself shows us that it is linked to only one location inside Active Directory, an OU called Domain Controllers. Only your DC servers end up inside the DCs OU, so settings in the Default Domain Controllers Policy only ever apply to DCs, but it is once again important to take into account that there are settings inside this policy and so they are applying to all of your DCs immediately upon creating the new domain.
The settings inside this GPO are fairly self-explanatory; it is a policy dedicated ...
