Speed = fun
No one goes sailing because it’s a slow sport. Otherwise they could lash the third reef in the lightest of winds. Depending on how ambitious you are, every boat on the horizon is an “opponent”.
More speed = greater distances
It may seem trivial, but at higher speeds, you can reach farther destinations on your holiday.
Speed = safety!
Higher speeds help you to avoid or escape bad weather.
Their potential speed allows catamarans to accelerate in waves, thus reducing the danger of capsizing. See daggerboards.