Prior to iOS 10, your iPhone, iPad, or iPod touch would try to automatically maintain a minimum amount of free space by removing unnecessary files from local storage under certain conditions. Included in this list of “unnecessary” files were things that Apple reasonably deemed could be re-obtained from the cloud — including items in your iCloud Music Library. Naturally, many users found this inconvenient, and Apple has obviously heard their cries — in iOS 10 you can now either turn this feature off entirely or choose to ensure that a minimum amount of music remains on your device.
You can find all of this under a new Optimize Storage setting in the Music section of the iOS Settings app. There, you’ll find a switch that can be used to toggle the feature on; when it’s enabled, a list of minimum capacity settings will also appear. The settings will allow you to set the minimum amount of music that will be kept on your device when space runs low. Selecting None here is the equivalent of the standard behavior from prior iOS versions.
A new Downloaded Music section can also be found above the Optimize Storage settings, which will show how much space your downloaded music is consuming on your device. Tapping on this will take you to a more detailed list showing you how much storage is being allocated to each artist on your device. From here you can see individual albums and tracks, and delete the local downloads for any artist, album, or track using the standard right-to-left swipe gesture.