A workflow can complete and still answer the wrong business question. Validate its output against the source grain, expected population and intended measure. Join exceptions explain source coverage. Duplicate-key checks explain multiplied records. Summarized counts help you compare populations before and after preparation, but a count alone doesn't prove that values landed in the correct columns.
Keep a clear rule for what counts as an exception. A credit can be a valid sales record, while a missing team may need a staffing review. An empty exception table can be the correct result when no records violate the rule. Don't force an exception row into a clean file. Build checks that work on the next extract as well as the visible one, and report the evidence rather than treating a green run message as approval.