Thanks for the clarification! I explained one of my usecase in this threat:
At the moment I am trying to understand how to control how much data is downloaded if only parts of the file are requested for read.
In this case I would like to download and store the whole file or at least bigger pieces, even if only tiny pieces are requested one after another to limit API Calls and I am trying to figure out if the cache backend is better for this or the vfs cache.
I hope you don't mind the cross post – I think in general I want to achieve the same thing as the OP, but I made the other threat because I am also interested to find out more about the caching mechanic and I hope somebody can clarify it for me.