The global group "Domain Admins" is automatically placed in the local Administrators group automatically when a computer joins the domain. This group may not be beneficial when working a "Master Domain" model because the you can not add master domain accounts to the "Domain Admins" group of a resource domain. In this case you would have to add the "MasterDomain\Domain Admins" group to the computers local Administrators group.
Also when users get Admin level access to their computer many remove the domain "Domain Admins" global group from the Administrators group. In that case it would have to be added back when the user is removed.
