IMO, there is only one benefit - you can keep all your QVC purchases straight by having all the charges in one place. If that makes life easier, then it's a benefit.
Obviously, the high interest makes it only sensical if one pays the entire balance each month. I only happen to have a Q Card because they sent me one, some 15 years ago when I used to purchase a lot, without even having my ss#. I use it for any QVC purchase so I will know quickly if I'm buying too much. I pay it off each month and it's never much at all.
Oh, and I also don't have to have any other method of payment on record here, so I don't have to worry about the instability of this website causing me to have a hack.