What happens after researching everything

In many games there's nothing useful to do and the player may scrap research centers to save maintenance costs and/or devote the resources to something else (Space Empires series).

In the Civilization series researching "future technologies" increases a player's score. It also raises the health and the happiness in the empire. One of the last few technologies enables a "wonder" project, space exploration, that in turn triggers a race for technological victory. In the Galactic Civilizations series (no relation) the final technology solves the nature of existence, and is victory.

In the Master of Orion series more advanced research reduces the size and cost of spaceship components, and "hyper-advanced" research in areas which have military applications therefore enables players to build more high-tech weapons into a given ship size and at lower production cost.

In Rise of Nations, the final four technologies result in such an advantage that the game will likely end quickly. Also, the "knowledge" resource needed to research is also used late in the game to produce cruise missiles and nuclear weapons.