I use a lot of expensive thread.
I waste even more. In this picture there are five kinds of conductive thread. You can identify the stainless steel thread because of the whiskers. Those pesky short circuit makers!
I keep a scrap box of tangles, tails and tatters. When sewing small repairs and adding hardware to and electrical trace I use these short lengths. This keeps my good thread on the spools for large projects and the scraps out of the landfill.