I use a lot of large "pieces" ..... scraps if you will......I do somewhat coordinate them but not with the front so much,....more with each other. I also love to use flannel if I want the quilt to be a bit warmer and softer. Sometimes I coordinate extra blocks into the backing. I generally feel that almost anything goes as long as it doesn't loundly fight with the top.....now a special top is different. Then I do try to make a nice and somewhat coordinating choice,