In plain terms
It answers one question: prove it. Not that you meant to run the cycle, but that you did, on these dates, against this list version, with these counts and these decisions. A useful trail records the pull, the match counts, each deleted or exempted determination with the person and timestamp behind it, the generated status file and its checksum, the submission, and the confirmation that came back. Chaining every entry to the one before it means a later edit shows up instead of passing unnoticed.
What it means for a registered broker
You will need it in two situations, and both are bad times to start building one. The first is a question from the agency. The second is a customer or their counsel asking what happened to one specific record. Keep the trail exportable in a form a lawyer can read and a machine can verify, keep it somewhere that survives a cleared browser and a cancelled subscription, and export a copy at the end of each cycle rather than trusting it will still be there when you want it.