can sync content from plex server to phone for offline viewing , it transcodes the content and is smaller on the phone.
the premium music part , just gives better meta data on the mp3's from what i can tell - does just pull meta data based on id3 tag , but on other parts of the mp3 - almost like Shazam for the meta data- so picks up alot of tags that was not completed. - called audio fingerprinting as per plex pass.
been messing with plex cloud , so my family can watch my content from cloud and not streaming from my local PMS as i don'y have decent uploads speeds , but fibre will make plex cloud pointless.
ah forgot the plex app in Kodi is nice - i prefer plex interface for local content over kodi , but the is just me , know some people like kodi's layout better. been using Plex forever and it is hard to adjust.