Those home ec teachers never realized how much damage they would cause by telling us not to touch the tension knob LOL! Tension seems to be the biggest problem for anyone who buys a professional quilting or embroidery machine. It is just something you have to get over, both for bobbin thread and top thread, at least if you want to use lots of different threads (which I do). Another thing you have to get used to is how much adjusting is needed. For example, my 12 needle embroidery machine tension needs to be rotated at least two full rotations of the knob before any significant change is made!
Think of it - is I reasonable for a machine to sew two layers of quilting cotton with a 50 weight thread using the same tension as 6 layers of heavy denim or a quilt with thick batting or the handles on a purse made with heavy interfacing and 4 layers of heavy canvas? You will definitely get a better stitch if you can adjust your tensions.
Pam