Unfortunately there are jerks out there that THINK flights aren't typically full these days and 'save' a seat for phantom friend.

My last flight in fact there was a guy in the row back and behind me one that was sitting against the window and had the Middle seat saved the entire time. There was a guy wandering up and down looking for a seat and actually asked the guy who said it was saved. Went up and down and asked AGAIN if it was saved and the guy finally relented that it there wasn't anyone coming..... Obviously cause he was the only one without and seat and the doors were closed..

Gotta love jerks like that!