Well, you CAN lift a centerboard out on shore if you need to for maintenance or something. But otherwise, when you are sailing, when it swivels up, it is hidden inside the hull. As Jake said, if you hit something, it is able to "kick up" into its slot, whereas if you hit something with a daggerboard, it's, "Uh-oh."

In other words, you never really see the centerboard and it is not in your way above deck. But there is a roller (or something) that goes along the slot on the deck, and that rolls forward or aft, depending on whether you are raising or lowering the centerboard.