By default, a user's policy settings come from the set of GPOs that are applied to the user object in Active Directory. However, in the Horizon 8 environment, GPOs apply to users based on the computer they log in to.
When you enable loopback processing, a consistent set of policies applies to all users that log in to a particular computer, regardless of their location in Active Directory.
See the Microsoft Active Directory documentation for information on enabling loopback processing.
Note: Loopback processing is only one approach to handling GPOs in Horizon 8. You might need to implement a different approach.