So you've got a fleet of four troop transports parked outside an enemy planet. Your frigates wipe out the rest of his orbital fleet, leaving that nice, juicy, PQ 20 ready for invasion.
You take a look at the options for invasion. You have 2,000 troops. They have 12,000 defenders. Your advantage factor is 5 to 1, not quite enough to be assured of a win. It would be great if you could use mass drivers or tidal disruption, but you don't really want to ruin those nice improvements your enemy had set up for you already. Maybe you could use mini soldiers, or information warfare, but that's so expensive, not to mention it's less effective to lower the enemy's advantage number when it's already so low.
Then it hits you: metagaming can help.
You've noticed that the game only records planetary damage after your invasion succeeds: on a failed invasion, you haven't really seen any planetary damage incurred. You split your fleet of four transports into one fleet of three and a singleton in reserve. You go for mass drivers and send in your 1,500 troops. Against 12,000 defenders, there's not much of a chance to win, but they reduce the planet's defenses to about 2,000 troops (that 100-200% boost to attacker advantage helps a lot.) Against 2,000 defenders, your 5-to-1 advantage with 500 troops is more than sufficient. You switch to Traditional Warfare for the second wave. Your 500 troops invade and wipe out the defenders: there are only 50 or so survivors in the invading force, but that's more than enough to secure the colony.
Best of all, you now have your very own PQ 20 in all its glory to call your own. And look! It was the enemy's research capital! Time to go for Huge Hulls. . .
Aren't you glad you exploited a game mechanic to your own twisted ends?