I did it for increased tire clearance when I get around to getting wider wheels and tires. You don't have to, the axle is wider than a stock a-body one...you would only have to move the spring pads in 1/2" per side if you weren't moving the springs.
That being said, I don't think this would work so well in anything but a Duster/Demon/Dart Sport and maybe a 67-69 Barracuda