They are meant for use of a precut, be it a jelly roll, a charm pack, or layer cake. Occasionally, yardage is needed for some part of the quilt. It is easy enough to make a quilt larger or smaller by simply making more or less blocks, therefore needing additional precuts. I rarely make the size listed in the pattern. I make a lot of queen size quilts, and it is very easy to estimate how many more blocks needed just by figuring the block size listed. I made Jenny's Rhombus quilt for my DGS for his first apartment in a queen size. What a challenge that was, but DGS was thrilled and that is all that matters. I have lots of precuts in my stash, so I get lots of use of Jenny's magazine. I have made the Crosswalk Quilt about 6 times, and each time it looks different than the previous one.