The carousel rotisserie is a different way of grilling by using the burn box as a heat source.
Different grates can be adjusted to the desired height settings or can be removed and the spid utilized as a gyro. The intended heat source is the burn box in the back, which makes a wall of heat. The bottom tray can among others be used as a drip tray to collect juices, as a frying pan or fill it up with coals as an alternative to the burn box.
The thought behind the vertical system is, that fat and juices can drip down from the top and help flavor and baste the layers below.