Yes, in the long run, yardage is less expensive; however, there is so much variety in a charm pack or a layer cake. Many of the quilts I do call for using a layer cake square which can be cut in half or quartered. I like the variety, so I tend to use them. I'm such a "crazy" quilter that I don't even mind using the leftovers from a quilt top to piece the backing and incorporate many of the scraps I have on hand.
It seems that this discussion is like many of them in the quilting world: do what is most comfortable for you, but use the best materials you can afford.