DAX: When to Use a Measure Instead of a Calculated Column

In DAX, a calculated column is evaluated row by row and stored in the model, while a measure is computed on the fly based on the visual's filter context. Simple rule: if the result should change based on the filters and slicers applied to the report (a sum, an average, a ratio), use a measure. If you need a fixed per-row value to sort, filter or build a relationship, a calculated column is appropriate. Mixing the two up is the most common cause of slow dashboards or inconsistent results.