From the back of the book:
Not all participating democracies will be identical. Each will have its own eccentricities and nuances. The same applies to the corporations players will take jobs for or purchase from. Not all agricultural companies are run the same way, after all.
By using the provided corporations, governments and religions in this book, referees will be able to populate their universes with the minimum of effort, ensuring now that not only every starport is different, but the world beyond its gates remains vivid and alive in the minds of the players.
The goal is to make every planet in your campaign unique and interesting, and Supplement 15: Powers and Principalities will do just that with no extra work on the part of the referee.