If Spotify would just implement the option to point it's offline music to the SD card.
There are hundreds of posts with complicated directions on getting this feature to work. Sometimes they work, sometimes they don't. In all instances you have to redownload your whole collection at least once and more than once if you can't get it to work properly. How hard could it possible be to add this to the app features? It's not like you guys don't have engineers constantly working to improve the app, because I genuinely appreciate the app updates almost every week.
Google Music does it. RDIO does (..or did) it, not sure if Apple Music does, but it probably does.