Certain environment variables at the time "nix-build" is executed can affect the nix configuration. Nix flakes default to ignoring those environment variables.

Certain environment variables at the time "nix-build" is executed can affect the nix configuration. Nix flakes default to ignoring those environment variables. Flakes are also the way forward for pinning nixpkgs; it autogenerates a list of revisions used to pin, and allows easy updating. Flakes and niv, to a large degree, are about solving the same problem.