The difference is that the lazy evaluation needs to be baked in. There are many scenarios in the nixpkgs code-base where lazy evaluation is used on a not-packag

The difference is that the lazy evaluation needs to be baked in. There are many scenarios in the nixpkgs code-base where lazy evaluation is used on a not-package level. For example the NixOS module system depends heavily on it. I haven't used Guix to be able to compare but it saved my life many times. I suspect the advantage for Guix is that it forces things to be better structured.