I had never worried about this either until I bought my Bernina & that was the first thing the teacher told me + never use compressed air to clean out the bobbin area of your machine/serger. It blows crud deep inside & moisture from the aerosol can build up inside your machine & lead to rust. I firmly believe in being "safe rather than sorry" . I realize some people are going to say "I've been pulling my thread up from the needle for years & nothing has happened" but why risk it? Even if your remember only some of the time, it's worth not having a service call. Old habits are hard to break but why not try.