You most certainly do.
While it’s tempting to try and save a little money, your hot tub cover is much more than just a visually appealing accessory. It traps in heat when not in use, which not only lowers your energy consumption but your energy bill as well. It prevents evaporation, which helps you preserve the water you have and the time it takes to refill your spa. It also keeps out leaves, seeds, and other debris that can dirty up the water and clog your filters.