Extending Access to Child Groups
By default, when you add a group to this policy, access restrictions will only apply to members of the selected group.
Under some circumstances, it might be necessary to allow access not only to the group itself but to any child group in the hierarchy. For any group added you can mark a checkbox Extend to Children in order to extend access to child groups.
In the example above, the policy is granting access for any user member of IT or any of its children.