Policies are mainly used for the governance of resources. Azure Policy is a service in Azure by which you can create, manage, and assign policies in Azure. These policies can be used for auditing and for compliance. For example, if you are hosting a secured application in the East US location and you want to limit the deployments in East US only, Azure Policy can be used to accomplish this.

Let's say you don't want to deploy SQL servers in a subscription. In Azure Policy, you can create a policy and specify the allowed services, and only they can be deployed in that subscription. Please note, if you are assigning a policy to a subscription that already has resources, Azure Policy can only act on resources that are created post assignment. However, if any of the existing resources before assignment don't comply with the policy, they will be marked as "non-compliant" so an administrator can rectify them if necessary. Also,...