When manually tightening lug nuts, it's surprisingly easy to over do it. It's possible to strip or break wheel studs, and even warp brake rotors. Both are expensive to fix, and the latter has the potential to be extremely dangerous. Use of a torque wrench helps avoid such problems.While they certainly do use air tools in pro shops, and there's nothing like an impact wrench for breaking a stubborn nut free, the tool has a built-in clutch that's used when replacing your wheel, to avoid over-tightening.