i wouldn't hesitate for a minute to use a 3/4 impact to remove a bolt but install is another matter. proper torque and then 90* more is the only way to ensure that crank bolt stays on. no way you can do that with an impact wrench. much the same way with rims. would you use an impact to install your wheels then make a high speed run? or would you torque the aluminum wheels with a torque wrench to ensure you don't over torque them and crack a wheel?

theres always a quicker way but in the end it may be a better way