Organisms of all types are classified to make it easier to identify species of plants and animals, to help sort and track similarities and differences between different parts of various kingdoms and to help scientists determine the relationships between currently known species and new ones. Modern scientists use these classifications to help understand species, both new and old. It allows them to be able to link the current evolution of a species to its ancestors and perhaps predict what changes could come in the future.
Since there are millions of species on the planet, trying to keep track of them all without some sort of system would be nearly impossible. It is important to keep track of various species and their relations because it can be a great indicator to the state of the world. Many species of bacteria and indicator species of animals can tell scientists if an area is becoming unfit to live in. Being able to track how these same species might evolve under certain circumstances is also important.
Many species on the planet are similar enough to humans on various levels that the failure of a species can be used to indicate danger to a human. An example of animals indicating that life is unfit for humans is the use of canaries in mines before the electronic gas detectors were available. The birds stopped singing or died and the miners knew they had a gas leak.