Taking a planet, and policing a planet, are VASTLY different operations. A few guys throwing asteroids can take a planet. Policing that planet would likely take around one operative per 100 population.
Neither the Republic nor the Empire had the habit of "taking" a planet. The Republic was a federation of almost independent planets, and the Empire used the same structure with just a random intervention here or there if one tried to actually act independently. And the Empire interventions were much more on the lines of "destroying" than "taking".