The need for extra alternator output comes with people who run snow plows that have extra lights to run as well as power the electric over hydraulic lift for the plow. Overlanders use the extra alternator output to run electric air compressors, winches, and other electrical accessories. The thing to remember is that the battery in the car is a power reservoir used to start the car not run other electronics. The alternator is what runs the electrical components in any vehicle, and top of the battery after it has been used to start the engine. When you start running aftermarket accessories you can easily use all the alternator’s capacity and drain the battery, hence the need for an alternator with a larger output.