Trace a number back to its source
A report might show total sales for a month. That total may come from individual orders, with refunds subtracted and amounts in other currencies converted. Data lineage maps each step, from the original records to the finished report.
People can document the steps, or data pipeline tools can help record them. If a source changes or a total looks wrong, the map helps a team find affected reports and trace the problem.
Keep the map current
Manual spreadsheet edits or undocumented scripts can leave gaps. Lineage shows where a number came from, but it cannot prove the original records were accurate. Teams need to update the map when the way data is handled changes.