I haven't tried it first hand.

I've written over ~10k lines of Ansible playbooks and roles to fully automate setting up servers to deploy Docker based web apps, so I do like the concept of declaring the state of a system in configuration and then having that become a reality. I know NixOS is not directly comparable to Ansible but in general I think IaC is a good idea.

It was important to me that my dotfiles work on a number of systems so I avoided NixOS. For example, the command line version works on Arch, Debian and Ubuntu based distros along with WSL 2 support and macOS too. The desktop version works on Arch and Arch based distros.

Beyond that, I also use my dotfiles on 2 different Linux systems so I wanted a way to differentiate certain configs for certain things. I also have a company issued laptop running macOS where I want everything to work, but it's a managed device so I can't go hog wild with full system level management.

Beyond that, since I make video courses I wanted to make it easy for anyone to replicate my set up if they wanted but also make it super easy for them to personalize any part of the set up without forking my repo (but they can still fork it if they want).

All of the above was achievable with shell scripts and symlinks. I might be wrong since I didn't research it in depth but I'm not sure NixOS can handle all of the above use cases in an easy to configure manner.