An Acceptable Use Policy is a high-level umbrella document that states what is permissible and what is not with an organization’s resources. However, it needs to be further translated into step-by-step guidelines, and to concrete technical and physical controls to ensure that the objectives of the policies are accurately enforced, without leaving room to interpretation, user memory, will, and discretion.
For example, if an Acceptable Use Policy forbids the browsing of adult websites at work, a user may still out of ignorance, or discrete defiance, visit such websites. The management has no way of knowing unless they monitor Internet usage in which case they are being for reactive to enforcing their policy, rather than proactive.
Further, if this leads to compliance failures, then the damage is already done and monitoring and log examination will not save the organization. However, if technical controls in the form of firewall rules and URL filtering were in place it ensures the compliance of the policies, and it is a more fail-safe way of enforcing the policy.