How the platform is delivered, source to dashboard. Each layer has one job, so failures are isolated, transforms are testable, and every reported number is traceable back to where it came from.
The medallion split (Bronze/Silver/Gold) isolates concerns: ingestion problems stay in Bronze, quality logic stays in Silver, and business logic stays in Gold — each independently testable. Pairing that with one Power BI semantic model is what kills the "four different totals" problem: definitions live in exactly one place, so a metric means the same thing in every dashboard, and governance (security, certification, lineage) is applied once rather than per report.