An interesting read about the consequence of trying out Apple Music and not reading all the small print in detail. It turns out that when you turn on Apple Music you also turn on the iCloud Music Library which allows the Mac to copy your audio into iCloud. However in doing so Apple does not necessary store your copy of the file, especially if it believes that it already has the track stored within its library. This could potentially lead to the lose of data.

In addition to the risk of data loss you may also find that when you end your Apple Music Subscription, you will loss access to audio purchased outside of iTunes due to loss of access to the iCloud Music Library.

More details online.