They are pretty useless, but theoretically you could get some use out of them if you've got farming bonus tiles. A planet's morale bottoms out at 25 billion population, so if you can somehow keep the morale up just enough to keep it growing after 25 billion, it will never stop growing. Then theoretically that ctr. would be useful.

Also you have to consider the initial colony's farming. It only takes one +300% farm tile to pass the break-even point, because that's the equivalent of 4 farms + your initial colony. But still, as it is now, that's far more food than your morale can handle. If only you could export food....