When would you use a sealed class instead of an enum?

This tests your ability to model complex, heterogeneous states. A great answer explains that sealed classes define a restricted hierarchy of types (like Success(data)), allowing each state to hold unique data. Enums, by contrast, are a set of singleton instances. Both guarantee exhaustive `when` checks. A common red flag is failing to grasp this fundamental state-holding difference and treating them as interchangeable.