These aren't precisely the specified goals of Nix, but things I appreciate as a consequence of its design:

    (1) If a build works on any machine, it will work on yours. Package builds are isolated and reproducible. For example, setting up Plasma is as simple as `services.xserver.desktopEnvironment.plasma5.enable = true;`, every time, in every environment.
    (2) Environment configurations are declarative. You will always know what a given host or shell has installed because you have to write it down.
    (3) Nixpkgs is _by far_ the largest package repository of any package manager, and packages are updated very quickly.
    (4) With home-manager, software can also be configured declaratively; my preferred tmux configuration will always stay in sync across all of my machines because it's managed by Nix, not ~/.tmux.conf.

Following (1) and (2), executing[1]

    $ git clone https://github.com/xyz/nix
    $ nixos-rebuild switch --flake ~/nix#host

On a fresh NixOS install will create an environment identical to that given host.

[1] Don't quote me on the specific syntax. But it's roughly this simple :)

Addendum: And as a consequence of Nix being separate from NixOS, if a package builds in Nix, it will work on any distro.