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 7 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.
Loopback processing is only one approach to handling GPOs in Horizon 7. You might need to implement a different approach.