I learned this in Home Ec as well. I think I have mostly used it because when I made all my clothing, I used thread to match everything. I would cut the thread at the spool, tie it to the next color thread I wanted to use and pull it through right before the needle. Then the new color would be on and no total threading of the machine. We did the same thing when I worked at a custom embroidery shop. You wouldn't want to have to thread all those needles if you didn't have to.