What does Spotify cache in /Storage?
I think there's more question than answers there but it's Spotify's cache of files consisting of:


streamed music saved locally
imported songs (your local music)
adverts
metadata


The obtuse naming convention is purely a method to obfuscate the contents of the cache.

The cache is used in multiple cases, the main ones are:


to play already downloaded files instead of re-streaming (saves their bandwidth therfore saves $$$)
to allow Offline mode for Premium accounts