Also, once you have your base install working, then futzing around is super cheap and almost riskless [1]. You can completely brick it, discard it, try again,

Also, once you have your base install working, then futzing around is super cheap and almost riskless [1]. You can completely brick it, discard it, try again, and/or roll back to your working base system with very little cost in time and effort. It enables no-cost rapid iterations in your system config. [1]:the only risk is that once in a blue moon, a major version Nix upgrade will change Nix's database schema, and be incompatible with prior builds of lower versions, so you can't roll back to a lower version build after such an update. But afaik that's only happened a few times in Nix's history, is not a surprise, and is communicated well in advance.