the seats they install. If you put them on properly you don't take up any extra room (by having the metal bars hooked under the bench so it can't move anywhere. I had a guy in front of me that didn't and was scooting too far back and I had no room for my legs.
I have to have a seat with a back. My back is toast by the end of the games if I don't have one. My row also doesn't have anyone directly behind me so I can lean back far as I want. It's nice.