Your expense-categorization schema uses an enum field with five categories: Travel, Meals, Office, Software, Other. About 20% of expenses end up in Other, and the analyst can never tell what they actually were — "Conference registration", "Subscription renewal", and "Recruitment fee" all collapse into the same opaque bucket.
What's the best schema improvement?
Why did you pick that answer? Two or three sentences. The act of articulating it is what builds the judgment — not the click that follows.
Enum + "other" + detail field is one of the cleanest patterns for extensible categorization. The enum gives you parseability and consistency on the common categories. The other option gives the model an honest escape hatch when nothing fits. The paired detail field captures what other actually meant, so the analyst can both group ("how many Other cases this quarter?") and inspect ("what were they?"). You get rigid categorization where you have it and graceful handling where you don't.
Free-text categories destroy downstream aggregation. Now "Travel", "travel", "Trip", and "Business Travel" are all different categories. Enum + detail keeps the structural advantage and adds flexibility only where needed.
Removing Other doesn't eliminate the misfit cases — it just forces the model to mis-categorize them. A Conference registration becomes "Travel" or "Office" in a way that obscures rather than illuminates.
Adding 30 more categories chases the long tail with diminishing returns and introduces the new problem of overlapping categories the model has to choose between. The detail-field pattern handles the long tail without exploding the enum.