Don't tell anyone, but I'm a bit of a control freak. When I wind bobbins, I hold the thread as it's winding on the bobbin. I'm sort of an extra tensioning device. Usually it's because the bobbin doesn't fill evenly, so I manually guide the thread back and forth. Sometimes I just want some extra drag on it so it's as full as possible. I think it's a holdover from winding balls of yarn on my ball winder.