zas - most people do not have multiple terabytes of spare disk space on their hard drives to dedicate to picard cache. If every application I had installed on my PC needed several hundred MB of cache, I would very soon be out of disk space. And it does not make any real sense to have a cache which is on the order of 1% of the size of the music collection!!

My measurements show that with a sufficient size of cache (so it doesn't wrap) then you can save c. 90% of the download bandwidth without forcing - but you are still limited to the 1 request per second to check whether the data has changed, so it is not much quicker.

With forcing, it will read the cache as fast as it reads the existing tags from your collection!!