You can also push deployments to remote systems which is great for servers and headless devices like raspberry pis. I use colmena and deploy-rs on different projects because they have some nice features but you can also do it with bare nix.

I have a repo for kiosk appliances that can build an SD card image for a specific device in a fleet (so no on device configuration is required) but it can also push out updates or changes at runtime. NixOS isn't perfect for embedded devices yet but works well for cases like this in my experience.