With my machine, if I don't hang onto the tails when starting a seam, the bobbin side of the fabric will often end up having a blob of thread stitched in. I start my seams with a small scrap of fabric leader, so the blob ends up there, and my next piece is clean and tidy. To hang onto the tails, I need to pull out about 3" of thread; with my scrap, I'm sewing less than inch, so I'm actually saving thread.