The light weight of an impact driver is deceptive. When driving screws, these tools require far less force because the hammer and anvil do all the work instead of your shoulder and arm.
In this video, Gary Katz, Reseda, California, contractor and writer, demonstrates why, when it comes to driving drywall screws, there’s no better tool. An ordinary drill/driver is susceptible to stripping the Phillips head, but because of the action of an impact driver, the bit rarely jumps out and the head of the screw remains pristine.
For a comprehensive evaluation of these drivers, read Gary’s review, Cordless Impact Drivers.