With some of the newer machines, there are a lot of possibilities. I had a Pfaff 1471, took classes at the dealers.
There were a lot of new techniques where you HAD to change the tension. Ribbon embroidery comes to mind.
I now have a 2144. The workbook has stitches where you have to change the tension to get them to work right.
Rolled hem is one.
Most of the new machines go back to default when turned off. You usually have a place to save that stitch setting.