slideout jacks?

I've got another question for you folks: Are slideout jacks needed on a camper that's going to be used for extended periods of time? The salesman we bought our '05 from says no, but looking around at different campgrounds, some do and some don't have jacks. I'm thinking up picking some up for him when i go see him the next time. Is it a waste of money or good insurance?
Re: slideout jacks?

so basically the damage they can cause pretty much outweighs the possible benefits? it's an 05 montana, i'm hoping it's up to par! it seems overall pretty well maintained. I was concerned about how much those slideouts can take once we go with him full time