That's a good point. When you're in the middle a whole bunch of sail material, trying to carefully sew inch by inch, the last thing you need is the machine taking off like a rocket. With the upgraded motor on my Pfaff 130, it can get going faster than I want if I step on the gas too much, often resulting in use of the seam ripper.
It also tends to start shredding the thread if you try to go too fast through a lot of layers. I have found that oiling the thread helps with this. A #19 or 20 needle also is a must to avoid thread breakage in thick material.