[williamvds]

I've got a simple use case: reproducibly building a random derivation from someone's Git repo.

If they haven't pinned nixpkgs, I have no idea at what point it _was_ building successfully. It's just dumb luck whether my system's channel is a compatible nixpkgs.

If it's pinned, great, I can use that pin until I'm bothered to bring it back to mainline. At that point I'll override the nixpkgs input and bear the cost of updating and maintaining it.

Flakes make managing pins those easier, through a nice(r) CLI, and a standard format for them.