What's the benefit of running a true A/B test with campaign

By testing multiple variables at a time, an A/B test gives advertisers information they can use to adjust their campaigns quickly based on insights.
By revealing whether their trial campaign drove user action that wouldn’t have taken place otherwise, an A/B test gives insights into user behavior.
By running a single campaign at a time, an A/B test allows for a true ramp-down period between each testing period so that results can be decluttered.
By running concurrently with an original campaign, a trial campaign controls for external factors, like seasonality, that might otherwise bias results.

What’s the benefit of running a true A/B test with campaign experiments?