@TesTeq In the Johnny Decimal system one of the core ideas is to have an index on the folder structure (not the individual contents in the folders). That removes the need to remember where what is. | Although that adds a step that you don't have when the single level folder structure is it's own index.
There is a numbering system used where I work that makes absolutely no sense () but there is something there when it comes to the frequently used folders - you know the numbers from memory. If you add a folder in between, you lose the association where the folder is located next to. And I know from experience this causes me friction.
I have a pretty good knowledge of the QC section of the Library of Congress system and a pretty good visual memory. I used to amaze graduate students by taking them right to the books we needed to refer to. I say “used to” because the head of our library system closed our departmental library this spring, and now there is no direct access to any of the books. Some recent books are available electronically through various mechanisms. I know that times change and we change in them (“tempora mutant, et mutantur in illis”), but I do sometimes think of the burning of the Great Library of Alexandria two thousand years ago, and what we are gaining and losing.