Why do you need Impact Driver in your kit?

Impact drivers are small, cordless drill tools that are used to loosen screws and nuts that can not be removed by a traditional screwdriver. The DTD170Z is a cordless Impact Driver, with variable speed control, powered by 18V Li-ion battery (not included) to supply energy to the brushless motor, to deliver up to 3,600 rpm, 3,800 ipm and 175 Nm of maximum tightening torque for a wide range of fastening applications.

They can be used on a wide array of jobs; everything from building decks to tightening some screws around the house can be made easier by having an impact driver.