I agree with many on this board - you should get what you pay for. However, that isn't the norm when you buy in most stores. I always "over buy" 1/2 to a yard. I figure it compensates for "those little opps I made a mistake" in life, and I put the extra in my stash. I can't always catch problems in material and I know that I can lose from 1-6 inches and never want to be caught short. I have overheard ladies in quilt stores many times say they bought exact yardage and made a mistake or the yardage in pattern wasn't quite right, etc. and then they couldn't get any more of that fabric.
Can't tell you how many times that my pieces of material stash has come in handy on different quilts. Actually, my avatar is made almost entirely from stash. I think I purchased 2 different colors in about 1/2 yard or 3/4 of yard - the rest of the top I had "left over" from other projects.