Thank you for introducing me to Johnny Decimal!
Btw, I witness, in an almost daily basis, the power of a shared classification system based on numerical IDs/prefixes.
My parents use a web app based on an old-school text user interface (the vendor translated the original Pascal code to a CGI-based web app). The multiple routines are identified by numbers, (kind of) following a certain organization logic. Routines can optionally be called directly by typing its ID instead of navigating menus.
The team's communication and work-flow naturally organize around this classification method. The vendor's support staff also use the same language. "You can find this in 938, that in 835, and then check the overall status in 104". Repetition + predictability provided by the underlying classification logic quickly imprints those IDs in users' memory.
Such a simple, ellegant system.
The one way my personal system diverges from the original is that I have a 3-digit prefix before the 2-digit category ID. 001 is my personal recordkeeping other than creative projects and has its own category tree. Then 002-499 are creative personal projects (non-work software and music). Software and music projects each have their own category tree template. 500-999 are work-related; right now, 500 is non-software-project info related to my current employer (interview notes, admin stuff, blog posts, other writing) and 501-599 are major software projects. I am guessing 600-699 would be my next employer, 700-799 the next, etc.