You sure about the Liberty? The ones I've seen had rollers in the center and on each side in the front.
Generally speaking, the decks on Zero-Turn mowers are suspended and the rollers on them serve only to prevent scalping on uneven ground. Personally I run them all the way up on my machines and rely on my own intelligence to avoid putting the deck in places that will dig it into the dirt. They tend to dig on turns and rip up turf if I run them lower, so actually do more harm than good. The bigger the deck, the more useful they are. So I wouldn't let the number of rollers make any decisions for me if you're not going over a 52 or 54 inch deck.