I was using Apple music A LOT and noticed that my free space had slowly been decreasing without me doing anything or downloading new apps, etc. I guess streaming from Apple Music still takes up space. So if you use Apple music quite a lot and notice your space is disappearing, just go to Settings and log out of the app store and itunes. As soon as I did that I had 3 more GB of free space. I logged back in and I still had the space. I had no clue streaming music from Apple took up so much space on the OS.