For many applications, reading the first bits fast are enough to be able to start using the file... like streaming media, running ffprobe, medianfo, and other commands.
So if we had a flag that would allow us to cache all files but like only 1%, so they are never accessed from "cold storage" it would make such actions like starting a stream, or running some commands faster, and then more data would be requested and added to the cache on the fly.
Does it make sense?