The place i think they really help is... I use pre-wound machine embroidery bobbins (NEBS). When the bobbin gets about 75% used, it starts to rattle around the bobbin case a bit. The washers help then. I just got a Long arm and I've noticed that when the bobbin gets low, it seems to do the same thing. i was thinking about getting some for the long arm. They are also called "Bobbin Genie". Do a search on this board. Seems like there have been quite a few posts on this recently..