Additional weight and reduced chassis clearance seem to be the biggest cons to installing an auto-leveling system. Some jacks will not have enough extension to level a 4wd vehicle without hanging low under the frame.
For me, I never owned a system like this and therefore don't miss it. However, I find I do very little to level out at most campsites and can do most of the leveling by choosing a level area to camp instead of trying to level something that is uneven. Two 4x6 wooden blocks or nested plastic blocks is all I have needed when camped on a slope.