Oh, for me it's about my play style. I spend considerable time planning my invasion strategies. I spend hours looking for a good, interesting map. Usually one with a choke point of enclosed system that I can make my stable base from. Then I rename all the points in the galaxy I'm going to take to form my borders, and heavily fortify those. When there is a planet, I think very carefully how many planets I'm defending, I like being somewhere around 1 or 2.
I don't normally think it's worth all the extra resources to have one extra planet if it's gonna extend my front from 2 to 3 planets or what not, so I take down planets and then capitalize on them.
Thats really why I like this game, you can get awesome front battles with some very cool logistics. I spend 80% of my time in the Galaxy Map.