What really happens when you sync your library with Apple Music
What really happens when you sync your library with Apple Music is that all you songs and albums are deleted from your local library and replaced with iCloud library items you have to download again. Despite what is said in some places, Apple's current info warns of this, it does not keep any of your local library items that you may have imported from CD's or Vinyl your own or other sources of mp3 files, like Amazon - you can or will lose access to these files, half of mine vanished, on any device now on Apple Music and if you turn off sync they do not reappear nor do most of your apple purchases. There are some online sources and older apple articles that state it leaves your already purchased or imported items alone, this is no longer true - it may all be deleted and replaced with only what is available in the itunes/music store that is only available when sync is enable, and when disable, it may all be gone.
This is a huge issue for those with large personal libraries already of user created songs and mixes, eclectic, vintage, or international audio files. There would be a work around for Apple as if you have home sharing, you will notice that a separate library per user is listed - so Music is capable of working with more than one library and thus the same method of local or iCloud libraries could be implemented.
After I disabled sync, I lost access to some iTunes purchased songs that were no longed available in the iTunes store, fortunately I backed them up. Again, you should not have to worry about having your existing library destroyed - very bad for long time apple users - this needs to be fixed with the above multi-library method. I will not be continuing my apple music subscription for this reason until it is fixed = too controlling!
Use caution when using this function, as it only adds the capacity to save songs to your library or playlist and offline play. If you do not enable sync, you can still access the songs via streaming as well as the radio.
