I use the prewound only for embroidery.
Different machines use different bobbin sizes. What works in one may not work in another. My 2 Pfaff's use different bobbins. So ... I love those round rubberlike bobbin holders. I have somewhat color coded them and then marked them with a permanent marker as to which machine and what thread type. Not, I an definitely not OCD ... just like to be organized and ready to sew!
ali