Error can vary more widely than just 5-10%. For example, the same careful measuring to within 5-10% at 1-cup will result in ~40% error at 1/4 cup. And also, people vary in their cooking ability, especially around reaching out to new recipes. It can be hard to get recipes to turn out right, and sometimes it's hard to tell what went wrong.
This is Joshua (who posted the original email). I'm glad to see so much interest in source control scalability. If there are others who have ever contemplated investing a bit of time to improving git, it'd be great to coordinate and see what makes sense to do - even if it turns out that the right answer is just to make the tools that manage multiple repos so good that it feels as easy as a single repo.