I moved from Debian unstable to NixOS this past Saturday. It's been...interesting. I'm fighting the urge to run screaming back to Debian.
I tried purging Git from my system last night as an experiment. Try as I might I couldn't get all references to it to disappear from the Nix store. I disabled it from configuration.nix and Home Manager. Removed all system and Home Manager generations except the current. Still there after various combinations of nix-channel --update, nixos-rebuild switch, and home-manager switch.
How did I not notice that??