Useful when backing out of a parking spot after the car has been sitting in the rain. 

And absolutely necessary as part of the 911 as a functional tool, with function coming first and form following. From the previous responses, I am clearly in the minority (perhaps even an outlier) on this. It goes back to the 911 I lusted after when I was a kid: an early 70's Targa with a rear window wiper, with the kink in the wiper arm...