My dealer was the one who told me this about 15 years ago. Supposedly leaves lint where you don't want lint. In design college I learned that thread is wound on spools to be used in a particular direction, and I have had trouble trying to sew from a bobbin used in place of the top spool. I think this may be related, but I'm not sure. I know that some of the older machines always had the tension disks engaged even when the foot was up. This could be what caused the problem pulling thread up instead of down. I now release the disks and pull the thread straight out from both ends, not down or up.