I agree, thread is thread. Use what works for you the best. Some will have more lint in one machine and very little in the next. Use what works with the fabric you are using. I use a lot of poly threads because I have a lot of it. I use it in my embroidery machine as well as my sewing machines. Works fine. Sounds like the teacher has her preference and thinks every one should use hers only. Take her advise with a big grain of salt!!