Oh my God what is THAT?

I just bought new wiper blades for my '02 Golf, and they're the types that replace all but the arm, not just the filler blade. After I removed the OEM blades, I noticed the one on the driver side has a big plastic piece attached to it. The piece is not there on the passenger side, though. Anyone know the purpose of this? I wanted to find out what it was for before I tossed it.

I believe it's an air damn that pushes the wiper against the glass harder at higher speed. It reduces the chatter of the wiper on the highway.

I originally replaced my wipers like you did, but saved my old ones... later I was able to find just the refills for the wipers, and I think they work much better.

Yup, its the spoiler for your wiper. At high speeds, it helps to keep the wiper pressed against the windshield so that it can actually wipe the water off.

Ditto. That's what it is: don't throw it away. And try and remember which way was "up" for when you put it back on. ( I didn't, and it doesn't work well at all upside down! )