There's a blog post going around from a guy who claims that when he subscribed to Apple Music, it uploaded all his music to the cloud--including music he composed--and deleted his original files, thus stealing his music and holding it hostage to his Apple Music subscription.
This is patently untrue. While seemingly no one can reproduce his situation, whatever happened to this guy isn't how the service is supposed to work. And the likeliest explanation is that guy deleted his own files, probably inadvertently.
Serenity Caldwell at iMore.com explains how Apple Music works, especially when it comes to music you already have in your iTunes library before subscribing. While Apple isn't completely blameless, because the complex dialog boxes can be confusing, they aren't doing what they are claimed to be doing. And why would they? The backlash would be horrific.