Some git pretty good at figuring out what lengths threads they need and have very little waste. Haven't sewn for awhile, but in one glance I knew the length thread needed, visual length, not measured by yard stick, divide the length up to usable lengths, cut, thread the needles, now, sit and sew. Thread may not be as expensive as it was. But, why squander it and lose good skills. You are making money by the second, or, losing it. Tailors who were careless with the thread given for the job, and ran out, had to pay out of their own pocket to finish. Different companies different ways of handling business. So many tailors were paid by the stitches. Faster tailors walked off with more money. When sewing machines where allowed it really didn't help the slow hand sewers.