another reason for the occassional charm pack is:
it gives you one of every piece of a collection- if you love a 40 piece collection but do not want to actually buy a cut piece of 40 fabrics the next best way to get a piece of the whole collection is to pick up one of the pre-cuts offered. then it's easy to pick out 4 or 5 pieces of the you love- and you have a little of everything to go with them.