Windshield Wiper Wing

I have a 2005 Outback. When I went to replace my driver's side wiper, I realized that the OEM wiper has a wing on it. It's about a foot long, looks like an airfoil, and it's pretty heavy. It can't be detached from the wiper arm. The passenger's side wiper does not have one.

I went ahead and replaced it with a wingless aftermarket wiper, and I haven't noticed any problem around town and on the freeways. I worried that it might lift at speed, so I kept the old one just in case.

But I'd still like to know: What's the purpose of that wiper wing?