I have always heard that too, but couldn't figure out why it would make a difference. As Holice said, the twist is the same. I found out as ckcowl, that the length of your thread makes more difference than anything. You really don't save anything by trying to use a longer thread. It frays and breaks after a point. when I hand sew my bindings i thread several needles at a time so i can keep right on sewing.