There are a number of advantages to fast-drying denim fabric, and not just that they'll dry off from socially awkward spills a bit faster.
Quick drying fabric will keep you cooler on a hot day, by speeding the evaporation process and cooling off the fabric, thus keeping you cool and comfortable. Cotton, by contrast, accumulates moisture, and dries quite slowly. It can still dry in the heat of a summer day, but not as quickly, and the fabric will feel warmer.
It'll be more comfortable in cold climates as well. Since the moisture doesn't have a chance to stay there, it can't chill your body the way accumulated moisture in the middle of winter easily could.
Fast dry times are also quite helpful for laundering the clothing, especially if you're planning on hang drying the clothes. A regular pair of jeans might take a whole day to dry out, whereas quick drying fabrics might be ready to go in a matter of hours, depending on the climate. This is also helpful for machine drying, which is not only faster, but less energy intensive as well.
So, with that in mind, here are some of the fabrics used to make fast drying, high performance, super comfortable jeans: