Take me for example. I cheating on a chemistry test, sure, but i will never need to know any polyatomic ions. I'm going to college to study computer science and I'm good at computer science, that's what matters. So, really, knowing that information or not knowing it isn't going to affect my life in the slightest.
So cheating really doesn't have a negative affect. However not cheating and getting a bad grade would have a few negative affects, even if most of those are short term.