haha I remember pulling mine out of both sides whenever I put my lift in.. don't know what they are though. maybe some kind of partition to keep debris away from the fog lights..?
Ha, I came across the exact same thing a few days ago. Spent 20 minutes trying to figure out how it clips in place and finally gave up and tossed it on a shelf. There wasn't one on the driver side so I had nothing to compare it to.
It is there so that when you hit something your bumper doesn't cave in... a couple months ago I was the victim of a parking lot hit and run, had to remove that piece before I could completely pop out the bumper from behind.