The rear suspension of the Cherokee uses a leaf-spring suspension (there is a more technically correct name for this - named after someone, but I forget what it is). Leaf springs are made of pieces of flat steel that are bent into a curve. Several of these curved pieces of steel, or leafs, are stacked together to create the spring.
The stock leaf springs are designed to provide a certain ride height, load capacity, and handling characteristic (comfort of ride).
Add-A-Leaf lifts are exactly what they say they are - they add a leaf into the spring that is very stiff and cause the stock springs to bend more than they normally would. This increased bend causes the vehicle to sit up higher, but due to the stiffness of the leaf in the kit, can deteriorate the handling characteristics.
From what I've seen, some people feel very strongly about type of lift versus the next. I 've seen a general consensus that new springs are preferable to add-a-leafs if you're willing to spend the additional money, but many will say that the add-a-leafs are just fine too. In the end, you have to learn about each type, decide what you think is going to work best for you (how you drive, where you drive, amount of time on street vs. time off-road, and amount of money you're willing to invest), talk to people who have different types of lifts to get their opinion, and go with what you think is right - If you make a mistake, you may be out a bit of money, but you can always change.
Hope this answered your question.