Write a line to a config file, yes. It's a consequence of Nix' goal of accountability, atomicity, and reproducibility. - If a package isn't listed in configur

Write a line to a config file, yes. It's a consequence of Nix' goal of accountability, atomicity, and reproducibility. - If a package isn't listed in configuration.nix, it isn't installed. That's powerful information to have. - If you want multiple systems to run the exact same set of packages, you can do that trivially by just pointing them all to the same configuration. I suspect it would be much harder to provide a fair answer to the question of why you _wouldn't_ deem it important to know what software is installed on your computer. That seems like a pretty significant pitfall of most operating systems.