Once Legitimacy is above a certain threshold other decisions become available, such as expatriate donations (you gain 1 military and 1 civilian factory for a year for 25 PP) and joint exercises (you gain a bushel of army, navy and air XP for 25 command points).
Might not be worth it if you are still filling government slots or saving up for worker safety, but later in the game the options are nice. I for one will move heaven and earth for air XP.
Thanks, I did not know what I might be getting for my precious PP. These sound pretty interesting.