If you use the Homebrew module for Nix-Darwin, running `brew` against the generated brewfile becomes the slowest part of a `darwin-rebuild switch` by far. In the fast cases, it turns something that could take 1 second into something that takes 10, which is definitely annoying when running that command is part of your process for configuration changes even when you don't update anything. Homebrew no-ops against an unchanging Brewfile are really slow.