Auto wipers have two applications: for when you suddenly get water on the windshield, for example a splash from a puddle caused by another car, and for speed attenuation during a rain. Some people can panic when the visibility from the car suddenly goes to zero and might not be able to manually turn on wipers quickly, while still driving without seeing anything in front. The attenuation keeps driver from playing with the wiper speed control in an intermittent rain, thus not getting more distracted from driving.