I can see buying a bolt of fabric that you know you are going to use. I would buy a couple of bolts in neutral colour (tan, white-on-white etc.) for backings. I would maybe buy a bolt of black if that had Kona cotton or something similar. I can't see buying a bolt of regular quilting cotton unless you intended to re-do your bedroom? If you did a quilt, bedskirt, pillows etc. you could sure use up a bolt quickly. You could also work out an agreement with a friend to split a bolt?