If you sync your library, it will wipe all your custom likes/dislikes for songs you sync manually via iTunes as well as wipe your smart playlists (blank them -

If you sync your library, it will wipe all your custom likes/dislikes for songs you sync manually via iTunes as well as wipe your smart playlists (blank them - until you sync your device to your computer again) Therefore Apple Music is literally unusable if you have a large library of songs not on iTunes (like indie electronic stuff) and don’t want iTunes to identify them and switch them to Apple Music songs.