"Make Available Offline" feature?
Does it use data? Even for the songs that I already have bought or have downloaded via a CD? I'm confused.
iPhone 6, iOS 8.4
Make Available Offline downloads a copy of the track to your library or device so that you don't have to stream it from the source each time you listen to it. Download while connected to Wi-Fi and it won't use any of your mobile data plan. Songs that were on your computer or device when you enabled iCloud Music Library should remain so don't need to be downloaded again.
tt2