The last time you used a drill to drive screws into 2x4's, did your arm get tired or sore from the constant pushing? If so, and if this is a common type of task for you to tackle, you might want to take a look at impact drivers for driving and fastening jobs.
Impact drivers are tools that are made specifically for driving and fastening applications, rather than drilling. This can apply directly to woodworking. Drills are more commonly thought of first when it comes to woodworking, obviously because they are specifically designed to drill holes, but other tools may be better equipped for the driving and fastening jobs.
So this sort of compares drivers to drills, but what are the specific benefits of using one for woodworking?
For one, a compact tool is going to be much easier to carry around, and the compact impact drivers on the market are designed to fit into tool belts and pockets, at least as much as possible. The portability and light weight can be a very important feature for many people.
Less fatigue issues is also another large benefit. Impact drivers do the "pushing" for you. I already threw out the "driving screws into a 2x4" example earlier, but this is a great example. With a drill, you need to push and put pressure on the back of the drill to drive screws into wood. With an impact driver, the hammering action does this for you, and all you really need to do is hold the driver in position. If you are going to be driving a lot of screws into a deck during one day, for example, your arm and hands will definitely feel a lot better come evening if you spent all day driving those deck screws with an impact driver rather than a standard drill.
The small size of the more compact models can also allow you to get into tight spaces much more easily. This might not sound like a huge benefit, but if you commonly have a hard time squeezing your standard drill into tight spots, you could probably use a more compact tool.
