I’m just tacking on to the existing responses, but for me, the huge benefit I get that no one else has hit on yet is automated setup of partitions, LUKS, ZFS on root, and zswap (mostly via disko).
https://github.com/nix-community/disko
It’s sooooo much nicer than wiring those up by hand.
And I have a custom USB iso based on the nixos installer, with has an ssh server running by default, with my pubkey already wired up. So I can plug in a USB to a new device, boot from it, run recon remotely to figure out how I want to set up the disks, then run a full install from my laptop over SSH with a single command (via nixos-anywhere).
https://github.com/nix-community/nixos-anywhere
NixOS is an absolute gem.