People have been using sheets for backs for years. However, there is a reason it isn't recommended. One is the problem with cotton and synthetic blends, but the real issue is that most sheets we want on our beds are soft, which usually means a high thread count. This high thread count makes needling through it a bear. This would be more noticeable with hand quilting.
I did make a quilt many years ago, using an old super percale sheet on the front and the back. I used a thermal blanket as the batting, and tied the quilt. Out of all my quilts that was the most heavenly one to use! My kids would fight over it, on son took it away with him, and it got snatched by another son. The quilt has been retired though, it was just way too raggedy!

I use sheets all the time. I wash and wash the quilts and they hold up really nice.

I am still kind of new at quilting. With that being said I have not wanted to purchase expensive fabrics until I get better, so I have used sheets for the backing. A couple of the quilts I have made didn't line up really well when I sandwiched them so having the sheet hang over a lot at least gave me extra room on the edges so I didn't end up short. Another thing I have been doing is purchasing thin blankets (almost the thickness and feel of felt) for my batting at $5.00 each. Because of my frugality I have not put more than about $50.00 into a quilt yet. I'm not necessarily being cheap so much as not wanting to spend a lot in the learning process. New hobbies can be expensive if you jump in a start with top of the line everything....just ask my husband how much he has invested in my various endeavors through the years! LOL

I quickly remind my husband how much his hobbies have cost over the years. Believe me, I have a long way to go to catch up to him....hunting, fishing, building truck engines and refurbishing an old Ford! believe me, I know expensive hobbies!! haha! You are smart to try to be frugal. Where do you find blankets for $5?? I never find bargains like that that I can use. Thanks!

I can never use that excuse. My hubby has NO hobbies! He does like old tractors but he actually uses the things for farming-he's a full time farmer. So not only is it for work, it's tax deductible. And he will only have one or two at a time, both of which he uses. If he wants a different one, he trades. He doesn't use electronics, doesn't care about clothes, fishing, sports, carpentry, etc. I wish he'd get an expensive hobby so mine doesn't seem so expensive. lol

My Long arm quilter uses sheets for the larger size quilts. My Mom always used sheets as long as they are 100% cotton and not real fine thread count. I have used sheets but I do not hand quilt. I guess to eaches own