I love charms! I have a terrible time matching fabrics so I love the variety of the charm packs. If I really fall in love with some of the pieces in a "line" I will buy additional 1/4 or 1/2 yard each of my favorite. But I only buy fabric - whether yardage or precuts - when it's on sale.
Oh - with rag quilts I love using layer cakes - I really can finish a Rag Quilt in a day with layer cake precuts!