why is it a bad thing that he has a sweet potato

Because Theo is a spaz and thinks of he does even one little thing not exactly how Sejun told him too he will get demoted. To be fair though, Sejyn manipulated him to be this way, so although a spaz, I don't blame him.

So basically, there is nothing wrong with it but They will likely need something up big, or accidentally do something amazing from his freak out over a single one of the crops being wrong. I personally think it will lead the locusts to the 99th floor, but that's just conjecture on my part.

Need = mess. “They will likely mess something up...”