the older sewing machines had the ability to disengage the needle head from the wheel, so when you wound the bobbin, you weren't 'sewing'. Some of the newer machines don't have this feature so you 'air sew' when you wind the bobbin. My mom got one of the newer machines and was used to the older version and was very concerned about running her machine excessively when winding a bobbin. Don't know if this is why your friend made the comment. Don't think it actually hurts the machine, although I did get a stand alone winder for my long arm because it was disconcerting!