[jahav]

MS stores windows codebase in a single repo (https://devblogs.microsoft.com/bharry/the-largest-git-repo-o...). 300GB.

I don't really see a benefit of having all code of an org in a single repo. Single product, sure. But whole company? Why. Not to mention, these are serious outliers.

From security standpoint, it doesn't seem great, from practical side, it's not great (bandwidth cost ect).

[Ygg2]

There was similar push by Facebook to improve Mercurial perf and they showed some impressive advantage over Git. It seems it was abandoned eventually for Git.