Azure Web App supports deployment slots. Production slot is the main one and there can be a couple of others. In order to follow a principle of least privilegesdifferent slots should have different security principals for deployment.
A service principal with deployment permissions for only a dedicated slot is useful in order to limit access to production deployment.
Sometimes we need to restrict access to some URL-path of a Web application from Internet while allow to access the whole web site. This kind of restriction might be relevant for example for a administrative user interface or a special API that should not be accessed from Internet.