I spent 3 years building a taxonomic database of plant specimens for the Missouri Botanical Gardens (http://www.tropicos.org/). Myself and two other programmers used a modern database and web pages to share the specimens with the research community. Last I looked there are over 3 million specimens included. Anyway I never got a straight answer as to why there is so much time, money and botanist's lives spent categorizing the earth's flora. What is the end goal here? I'm hoping there are professional scientists here that do taxonomic work that can chime in. Thanks.
Biology is about observation and learning from nature. If you categorize the species, it helps you in quickly understand what the species is about, what are some of its common characteristics, phylogenetics, etc. It has applications not just in understanding evolution, but in population studies, ecology. Why do we give humans names? So we can find them quickly and easily and associate them with certain characteristics. It is the basic human nature of using patterns to quickly identify objects.