[erik_seaberg]

If you're trying to upgrade or rebuild ten year old software, it's very important to know exactly what its dependencies were and where to find them, because there are too many other versions to choose from and most of them won't work. New software only needs a lockfile because it will eventually get old (if useful).

[castwide]

Fair point. But that just means the breadth of files that might need to be preserved is even broader than I suggested.