Rollbacks are a minor feature, I never found any use for in either Guix or Nix. The main advantage of both of them is that installation and 'making available'

Rollbacks are a minor feature, I never found any use for in either Guix or Nix. The main advantage of both of them is that installation and 'making available' are decoupled. Meaning you can install five different versions of the same app and it'll be totally fine, as they don't sit around in '/usr/bin/foo' and clashing with each other. They sit conflict-free in '/nix/store/${HASH}/bin/'. For making them available for use you have to add them to your profile/environment (i.e. $PATH and symlinks that point '/nix/') or just run them from their '/nix' directory if you prefer. This makes development and testing new versions much easier as nothing ever really breaks to begin with. You can just spawn a new environment, fill it with whatever you need and use it. And it all happens at the packaging level, so it's pretty quick and you never end up with snapshots that capture far more of your filesystem than you planed.