I’m unsure if this is satire, but you don’t rebuild a NixOS system every time you boot or SSH into it or something. It’s sort of like the Arch “assemble your own vehicle how you want” image except it allows you to do so on new hardware declaratively. Like having dotfiles for the entire operating system configuration that are processed by the OS itself. Also really nice for unattended remote installation with https://github.com/nix-community/nixos-anywhere