Comment by thaumasiotes

> As a layman, the only condition I'm aware of with this "downside but also upside" quality is sickle cell anaemia

Essentially all traits that you might think of as "traits" and not "features of the species" have downsides and also upsides. Where there's any significant imbalance, the genes for that trait will be purged from the gene pool (if the trait is basically all negatives) or sweep to become universal (if all positives).