That is kind of a niche use case ;) In the times when it was a real issue (I would hazard a guess that that means “before XP”) the reason was that the original

That is kind of a niche use case ;) In the times when it was a real issue (I would hazard a guess that that means “before XP”) the reason was that the original registry on disk format made every registry access more or less O(n) in bunch of things like the overall on disk hive size, total number of keys, number of subkeys in each of the keys along the path…