The transformations applied within Power BI's M queries serve to protect the integrity of the data model and to support enhanced analysis and visualization. The specific transformations to implement varies based on data quality, integration needs, and the goals of the overall solution. However, at a minimum, developers should look to protect the integrity of the model's relationships and to simplify the user experience via denormalization and standardization.
This recipe includes examples of protecting a data model from duplicate values and enhancing the quality of a dimension column via a relationship to a separate data source.
