I was running out of space due to downloaded/offline music, so I unchecked a bunch of albums/playlists so they would no longer be avaialable offline.  Although the music was no longer available to me offline, it didn't free up any space on my phone.  I had to completely clear out the cache through settings to clear up the space.  I then did it a number of times to test - downloaded one or more playlists, verified the size of the com.spotify.music folder, then deleted the playlist.  The com.spotify.music folder never changed size.  I even tried rebooting with no luck.

This is frustrating because I keep a few of the playlists I follow downloaded for offline use.  Spotify automatically downloads new songs when they get added to the playlist, but when songs get removed from the playlists, the data doesn't get removed from my phone so that floder size stays the same - it doesn't get any smaller when those songs are moved.  The only way to clear out the com.spotify.music folder and get it to resync correctly to only the songs I set it to download is to clear out the cache entirely, and re-download the playlist.

This is on an htc one m7, latest version of spotify.