Well, when you are having issues with your sewing machine, you will more than likely be asked, "Did you change your needle?" Then it will be "Are you using quality thread?" Don't make the mistake and buy the inexpensive thread at the stores. Sure they are at a good price, but really, will your items hold together? If you are selling your items the customers will remember you if your items fall apart pretty quickly!!
You can go to the above site and see the different strands of thread under the microscope. Pretty interesting. You want to look for one that does not have all those loose fibers that can and will hurt your machine later down the road!