Using GP to enforce a default setting - Good or bad?

Question

I have seen many organizations enable a policy and set it to the normal default value. As I understand, every policy you enable takes up processing time when GP is
applied. Why would this be done and what is the value of using GP to enforce a setting that would normally default?
Example: "By default, file downloads are disabled
for the Restricted sites zone. However, we recommend using Group Policy to enforce this restriction of the Allow File Downloads setting to ensure that users cannot download files when they are in the Restricted
sites zone."
Thanks! 
Charlie Newman

Answer 1

As other experts mentioned above, it is for GPO precedence order. But there is a tricky point which you have to consider about. When there are plenty of policies flagged as
"Not Defined" in domain controllers, it means
"This policy is not important for me, You can set this policy locally, I don't care client"
Mostly administrators apply a policy with default settings just to enforce them to the clients and prevent them from modifying those policies via
gpedit.msc . In that case when the Local Administrators modify the local policies they will be revert back once the computer or user gets authenticated to the domain.
Regards.
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