Fascinating discussions here. MTCW- My neighbor (also on this board) only uses the finest of materials and, once upon a time, would never use a sheet for backing. Her quilts are beautiful and sturdy. Perfection.
I, on the other hand, have used sheets as backing for years. I mix HQ and MQ. The only problem I've ever had was with a new poly/cotton sheet that was too stiff.
We've shared our quilt experiences and gone shopping together. She taught me about the texture check to eliminate poor quality fabrics and to make sure material will wear out at the same rate. I taught her to use this skill when picking out sheets at thrift stores.
That's always been my rule, "If it doesn't feel good against my skin, don't buy it." Now, she may spend the money she saves on backing to buy more quilting fabric! Both of us learned long ago to keep learning through the wisdom of others. Glad she's my "Fabric Queen" neighbor!