Impact gun on crank bolt?

In the video an impact is used to tighten the degree wheel down. I was under the impression no sort of impact gun should be anywhere near the crank. Is that not necessarily true?

It very much depends on the amount of force and common sense being applied when using an impact gun and since not all impact guns or users are created equal its best to advise against it. Also i think the commonly held belief that impact guns should not be used comes from a time when most crankshafts were made from grey cast iron which tends to fracture under impact loading something that the more recently used forged steel cranks are more resilient to.