Governors, Leaders and all others are nice additions that can vastly improve your planet/empire/diplomacy/espionage/armys and fleets.
Meet my favorite governor and watch his traits:
The image includes the dismiss button - maybe I find a savegame that includes my great leader.
Urctum 3 is the human homeplanet and financed most of my expansion with 35-40% tax rate.
The planet gives a third more taxes and is still maxed out in population with a very happy population - thats a good leders work.
And if IRC (manual & forum) the leader gave his greater boni to my whole empire.