For non-aesthetic reasons they are important, too. They help regulate the earth's energy balance, by reflecting and scattering solar radiation or absorbing the earth's radiated infrared energy. You undoubtedly know that clouds form when air rises and cools. When a blob of air goes up into an area of less pressure, it cools. When it reaches its dew point temperature, the rising parcel is no longer unsaturated.
Water begins to condense.
As it does so, it releases copious amounts of heat. So some of that cooling off due to its ascent is offset by the latent heat released by the condensing water vapor. What you may not know is that even if none of these things occurred, the fact that a parcel of air might pick up a greater amount of moisture than the surrounding air contains will itself make it rise. The reason why hinges on the concept of atmospheric stability. Such is the case when the environmental lapse rate is less than either the dry or moist adiabatic lapse rates.