I use ground combat... very useful when you're in a finite resources game. Take all your enemies' homeworlds, and they have nowhere else to get significant amounts of resources.
It's also nice to get population that can breathe a different atmosphere type. A Huge planet with a domed colony only holds 500M population and 5 facilities I believe, but 8000M and 25 facilities when the population can breathe the atmosphere. Comes quite in handy
