Coming from Ansible with hand-written config templates this was honestly a friction point for me - I felt like NixOS is trying to actively hide what it's actually going to configure. It's gotten better now that I read some nixpkg service sources but from time to time I still feel the urge to just directly manage my systemd units, sshd configs and whatnot. Like, sure it simplifies the setup but at the same time also puts another abstraction between me and the software I'm using.