What does an outpost on a planet do? I know asteroid belts have 3 choices of improvements, and on gas giants they provide helium, but it seems an outpost on an ordinary planet doesn't do anything. If they dont, then why offer the choice of building an outpost on one?
The only reason to build an outpost on an ordinary planet is to extend your logistical / supply range. It allows you to explore further out. Note that in addition to asteroids and gas giants, outposts are also useful on Black Holes, Neutron Stars, and Boson Stars as these can provide access to other strategic resources similar to Helium-3.