What are the key benefits of correlation between master ad and placement ad(s)?

The correct answer is "Applying changes to a placement ad only affects the placement ad." This is a key benefit because it allows for independent modification of placement ads without altering the master ad or other associated placement ads. This flexibility is crucial for tailoring ad content, targeting, or bids to specific placements while maintaining a consistent core message from the master ad. The other options are incorrect because: "Placement ads are duplicated together with the master ad" is not a benefit of correlation; it describes a potential behavior during duplication, but the core benefit of correlation is the independent management of placement ads. "Placement ads can be duplicated together with the master ad" is similar to the previous point and doesn't highlight the benefit of correlation itself, which is about the relationship and independent modifiability after creation.