A) "You foolish humans, those living planets were all that contained our outrageously massive battlefleet, which we shall use to invade your world"
B) "Well, Captain, we've destroyed all those living planets, and are heading home to Earth... Gasp NO!!! Earth was a living planet all along too! And the death of it's cousins has woken it up, and it's ANGRY!"
As opposed to "Thanks for saving us" "No problem, we're pissing off now because of course, on sixteen planets there's nothing we could possibly use to power us."