The other thing to keep in mind is not all fabric is entirely used in the construction of the project. It is the rough yardage required of how many ever colors or patterns of fabric.
Modern techniques of ruler/rotary cutting often leave unused ends, I also strip piece so have leftover strips sewn together as well.
Sizes of blocks or pieces can make things not cut well, especially if your fabric comes in a little short. Due to far too many bad experiences, I only figure on 40" of usable WoF (width of fabric) and when buying I buy a quarter yard too much (again, too much is better than not enough). There can be cutting mistakes, either by you or the shop, plus I wash my fabric and tear along the grain to get the true edge. Almost always have a 2-4" strip cut off grain.
Anyway, point of all of that is if you have something like 16" alternate squares, you can only get two of those per width (32"), so you could have a long strip of unused fabric that is too narrow.