My understanding is that the button toggles enablement of the sensor-driven wiper mode. If this is correct, it means every Tesla driver is betting their life and the lives of those around them that for every instance of something on the windshield blocking their view, either the sensor will accurately respond to it, or they will be able to navigate the touchscreen to activate the manual override before needing to react to developing conditions on the road. Given the reliability of automotive grade sensors (I’m not the only one who has paid mechanics a lot of money to tell me the sensor was bad right?) and the difficulty of interacting with touch screens, that’s not a bet I’d be willing to take. Looking at the German case, I wish more people were unwilling to take that bet.