Good vs Evil
How impactful is this in the long run?
The long run tends to be where it’s most impactful, but it’s not an arbitrary choice, it’s informed by your actions.
Positive alignment affects relations with positive-aligned free-cities and empires. Negative-aligned free cities and empires don’t seem to care. It’s neither beneficial nor detrimental.
Your elemental affinity impacts this a great deal as well. Order passives lean a lot towards things that work well with a high alignment, while chaos passives lean a lot towards low alignment.
For example, Order has a lot of stuff about vassals, while chaos has stuff to reward raiding provinces and razing settlements.