Pluto is the final generational planet. It spends so long in a sign that it affects everyone born within a sixteen-year period near the time of your birth. All by itself, it is not the most important feature of your chart, since such a huge number of people share this placement.
However, it does describe some general conditions that were activated during that period, and to a certain extent, you and those of your generation carry that energy forward with you as you mature and develop. Pluto is all about power, and the Pluto sign of anyone in power shows how they will wield this important responsibility. The Pluto-in-Capricorn generation (from 2008 to 2024) will completely transform the areas of government and big business, and some serious changes to the environment are bound to happen during this time. It will be decades before this group comes to power, but they will likely consolidate their political clout very early, and begin changing things from the ground up as very young people.