From an operational standpoint, it allows you to roll out a change in exactly the way you tested, confident that it will work the way it's intended. It also allows you to roll back or forward to any change with the same confidence. It also means you can restore a database immediately to the last known good state. Changes essentially cannot fail; no monkey-patching a schema or dataset, no "migrations" that have to be meticulously prepared and tested to make sure they won't accidentally break in production.
From a security and auditing standpoint, it ensures that a change is exactly what it's supposed to be. No random changes by who-knows-who at who-knows-when. You see a reliable history of all changes.
From a development standpoint, it allows you to see the full history of changes and verify the source or integrity of data, which is important in some fields like research.