There are a couple of reasons why you might want a mattress that’s thicker than 12 inches. Heavier sleepers and couples could benefit from the extra depth. Thicker mattresses offer more support than thinner ones. That means heavier sleepers and couples will get more lift and support out of a 14 or 15-inch mattress.
Mattresses with more depth also offer greater height. Those with larger bedrooms who need a luxurious tall bed to fill them out could benefit from a thicker mattress. Taller people who need a few extra inches to make their beds the ideal height might also do better with a mattress on the thicker side.