The biggest plus for an impact driver for me is the fact that they are so much easier on your hand & wrist. When drilling with a drill bit, your hand & wrist take the majority of the torque to keep the drill bit engaging. The larger the bit, the more force it takes to keep drilling. With a driver, the torque used to drive the drill bit comes from the driver. There is very little torque going to your hand & wrist. A good example is to take a powerful 3/4" drill and try drilling a 3/4" hole through a 10" pole. Then take a good impact driver powerful enough to drill a 3/4" bit through that same 10" pole and feel the difference.