In tyler's defense... I believe most impacts are rated off of a 1/2" hose, so they don't produce 'quite' the amount of torque using the 3/8" hose most of us have.
Other than that, I'll normally impact them on for a sec and then either torque them to the right spec or if I'm in a rush put it on FMPFT (Fat Man Pretty Freakin Tight)