I recently had a situation where that thing would have come in handy. I have a 3-ton flatbed truck, and recently had new tires mounted. The guy at the tire shop used a 1" air impact wrench to tighten the lug nuts. A couple of weeks later I decided to pull the front wheels and brake drums to inspect the brakes. It took me two hours to get the lug nuts off; they were torqued to more than 1,200 ftlbs. I had to use the 2 foot long lug wrench with a 5 foot long cheater bar and stand on it to break them loose.
A week later, I took the truck to a brake shop and asked them to pull the rear wheels and drums and inspect the rear brakes. The mechanic got out his handy dandy 3/4" air impact wrench (set on full torque) and proceeded to go at the rear lug nuts. He tried for 20 minutes to get the lug nuts to budge and finally gave up when his impact wrench broke.
Holy **** batman, those nuts were really twisted on! So, there really are situations where a monster impact wrench can be usefull.