Debian policy states that packages providing system services need to start those services by default, and that the starting of the service should be done by way of the /usr/sbin/invoke-rc.d script. This script will execute a program /usr/sbin/policy-rc.d if it exists, allowing the local system administrator to override behaviour if wanted by creating a policy script accordin to the interface specified and installing it under the correct name. This interface is however somewhat problematic, as explained in https://bugs.debian.org/911290. The package policy-rcd-declarative attempts to remedy these issues.

This package contains a default policy for policy-rcd-declarative that allows all services to start. Using it without any more specific policies is equivalent to not installing the policy-rcd-declarative package at all.