If you've lifted your Jeep with a larger suspension and oversized wheels and tires, the jack that came with your Jeep from the factory probably isn't the best suited any longer. Even if your Jeep is stock height, that factory jack really was only designed to work on flat, hard surfaces, like a paved road or driveway. A larger off-road jack can serve many purposes when you're off the pavement.
Besides offering high lifting ability, an off-road designed jack will be better suited to lifting your vehicle when you're on a soft un-paved surface. A new jack may also be able to function as a winch or come-along that could help get you out of a stuck situation.