The biggest mistake that I made buying fabric was buying far too many focus fabrics and not nearly enough blenders, tone on tones and lights. These are the only fabrics that I buy now and I don't know when I'll ever get some of my deep, intense prints used. Remember that new designs and colourways are always coming out and it is good to be able to say that you "need" some fabric and purchase one of the new collections. If your stash is extensive, more buying doesn't make much sense.