It helps to maintain your tension while stitching by preventing fabric from slipping on the smooth hoop. It's also great for those older frames that might have bent metal pieces... have you ever noticed that sometimes it's screwed as tight as it will go and still doesn't grip the fabric? Bulk it up a bit and give the outer hoop something to hold on to.
I just used a tiny dab of hot glue on the inside of the inner hoop to get it started. Then I wrapped it nice and tight. I finished it off with another tiny dab on the inside again. Easy-peasy.
Thanks for looking, I hope you have a creative day!