Many years ago I hand-quilted a quilt with a sheet as the backing. I'm sure it was a higher thread count than the cotton fabric, and it was miserable to quilt. Then a friend and I went together to work on a quilt for a mutual friend, and she bought a sheet to use as the backing. I washed it three times (probably not enough times!), and when I tried to use it on my longarm, it caused nothing but trouble with tension. I've found that using wide backing is much better - my machine likes it, and so do I. I'm happy for those who have used sheets and like them - it's just not something that works for me.