I found their raison d'etre very interesting.

"Declarative configuration management systems like Consfigurator and Propellor share a number of goals with projects like the GNU Guix System and NixOS. However, tools like Consfigurator and Propellor try to layer the power of declarative and reproducible configuration semantics on top of traditional, battle-tested UNIX system administration infrastructure like distro package managers, package archives and daemon configuration mechanisms, rather than seeking to replace any of those. Let’s get as much as we can out of all that existing distro policy-compliant work!"