Some designers make their patterns so certain units are cut from the LOF so there is no stretch. Bias has most stretch, WOF has a little stretch and LOF has almost none. So I have often seen outer borders or sashing strips in some patterns from LOF to have as little stretch as possible in that part of the quilt to help you keep it nice and square in the piecing process. I also cut these units first then the balance of my pieces from the remaining yardage.