Oh dear, I mistakenly used quilting thread on the top, and I ruined my machine beyond repair. I had to get rid of it, because it would no longer pick up the bobbin thread. It made a loud noise, as soon as I started stitching with it. I actually felt like crying.
I use those almost empty bobbins for my binding, when I tack it down on the back side. That little bit on the bobbin seems to go a long way, when I use it instead of a spool of thread for my binding thread. Of course, I do chose a matching thread, not just any color.