My 74 Chevelle has 'em. They're nice when your feelin lazy and dont wana work too hard to get out. Just hit the lever, swivel out and stand up.
Or if in a truck, jump down.
You cant have a very big center console because you need the clearance when the seat is sideways. I think a van seat would be better modified to fit a truck than a 70's GM "A" body bucket.