Just two weeks ago a mechanic used a 1/2" air impact to install the 8mm alternator bolts on my engine when preparing to run it on a stand. The alternator bolts originally threaded into the unique aluminum bracket. The original aluminum threads had stripped previously so I had helicoils installed. Everything was fine for years. I removed and installed the alternator multiple times with no issues. When that mechanic installed it he tightened the bolts so tight it pulled the helicoils right out of the bracket. They tried putting 5/16" helicoils in (and tried to charge me $150), but the bolts wouldn't even start to tighten, they just pulled right out.
Ford only made 250 of those brackets, so replacing it was not an option (and I had just had it powder coated). I had to take it to a machinist who installed oversized 8mm Time-Serts.
I have an air impact but I use it sparingly and mostly for loosening lug nuts and such. I use my air ratchet much more, mostly to save time as others have mentioned. YMMV
CobraRGuy