Good question! One of the main reasons we like to have the weight of the boat on the bunks is because they're designed to prevent damage when sliding onto and off of the lift. If the bunks are set too low, folks can damage the fiberglass on their keel when coming onto the lift if it's not lowered far enough into the water for the boat to completely float over it. The curved end of the bunks stick out a few inches past the lift which makes it easier to guide the boat onto the lift and they have more surface area to help distribute the weight evenly. The boat will probably be fine sitting on the keel but its the scraping when taking it on and off that we're worried about. The rollers avoid that of course.