I hate sitting down to do hours of work to find I have to replace the bobbin 20 minutes in. When I sit down to the machine, before I start quilting the first thing I do is check the bobbin. If I'm going to sewing for hours, I put in a fully wound bobbin. But if, like today, I only have a time to sew a few lines I replace the bobbin with a barely filled one. If it runs out, I can always put in a another one full or not, and then I've got an empty one I can refill.