If the review system would allow zero Stars that's what I would rate it. Hey YouTube music, here's a little explanation on what symbols mean. A check mark means that a task has been completed , so that when I ask a playlist to be downloaded, and the progress icon for that changes to a check mark, that means it's done. So why after it has been downloaded I'm told a song can't be played without using mobile data. If you can't do it don't check it off as being done.