Sample scenarios are used to test or verify the data model. After identifying the business rules and by creating some test conditions, you can "play stump the model" to verify/confirm the evolving data model. You populate your tables with some representative data and you identify what you expect the test conditions will show. This could be updating certain fields or having information required for a report. If any of the test conditions doesn't match your expected result, you must identify "what is wrong". Is it the data? Is it the data model? Is it the test condition? You must reconcile these and modify whatever is determined to be the cause of the analogy. Then retest until you are satisfied that the data model supports the identified business rules.