One of the biggest annoyances I have with doing this with Nix vs another tool is that Nix doesn't natively communicate back state changes so that you can make them reproducible.
If I make a git repo, place '~/.config/newsapp.conf' in there and then symlink it back to '~/.config/', if NewsApp introduces a new variable in its settings I am immediately aware because Git will complain about being dirty. However, Nix will happily just nuke that .conf and rebuild whatever is in your configuration, without letting you know about state. Which is ultimately bad for reproducibility. It's a huge blind spot in Nix.
If I make a git repo, place '~/.config/newsapp.conf' in there and then symlink it back to '~/.config/', if NewsApp introduces a new variable in its settings I am immediately aware because Git will complain about being dirty. However, Nix will happily just nuke that .conf and rebuild whatever is in your configuration, without letting you know about state. Which is ultimately bad for reproducibility. It's a huge blind spot in Nix.