There are definitely people who only use it on servers. Using NixOS on servers and Nix + macOS for the desktop/laptop is a somewhat common combo, too. But NixO

There are definitely people who only use it on servers. Using NixOS on servers and Nix + macOS for the desktop/laptop is a somewhat common combo, too. But NixOS is actually a very popular choice for desktop OS within the Nix community! That doesn't mean it's right for everyone, but it means that quite a lot of people who find Nix advantageous in other contexts also find it enjoyable or even indispensable for desktop usage. When I still had an HTPC/living room gaming PC, it ran NixOS. It ran Kodi, a bunch of emulators with EmulationStation as the frontend, Steam, and a Plasma desktop (KWin's built-in fullscreen zoom + a good Steam Controller configuration is actually a great interface for full-fledged web browsing on a TV!) and served me very well for years. It's the source of one of my favorite NixOS stories: one night my aunt was over to watch a movie with me, and I was running a NixOS system upgrade in the background while the movie played. It was a stormy night, and we had a brownout that forced the computer to reboot. Thanks to NixOS' atomic update procedure, the computer just booted right back up in a few seconds, and we put the movie back on! No need to troubleshoot or repair in order to get a working system. (I did later have to nuke some Nix cache which was corrupted by the process, but that affected only some of Nix's own operation and none of the application software or OS components that Nix managed on the system. Super cool!)