pro's: less pressure to the frame.
Con's: like already mentioned- if sitting for a longer amount of time, the tires loose air, the camper will lower, but the jacks don't.
biggest con: I truly believe, 99% of the people using them, have no idea what they do and how, damaging more, than doing good.
If I would have the camper stationary on a permanent lot, I would set the frame on brackets and get the wheels off the ground completely. This would be the situation, where I would use support brackets for the slide, because the camper would never move again anyway.
Other than that- neat gimmick to make the company rich, who sells them.
not on top of the "have-to-have-list".