It all comes down to your battle in space right? The first battle for a planet is the battle for orbit control correct? So I if I was to face a force superior to mine I would take out the capital ships that would inflict the most damage eg; Mon cal , SD etc. If you take out the ships that can bombard you from space you don't give then that option. It takes more then just one or two or three capital ships to bombard a planet. In another point if you do take out capital ships it lowers your enemys ground forces because these ships carry the most forces. Sometimes you must take it to the ground. Ground assult is the key you can't take a planet without it.

DLEM can't be bovved to come on the forum as there aren't many people who really can give an interseting convo for him.