What is the purpose of a publisher block list?

A publisher block list serves a specific purpose in media buying and advertising, primarily revolving around the management of ad placements. The correct choice reflects that the block list allows advertisers to specify websites or placements where they do not want their ads to appear.

By uploading blocked placements, advertisers can ensure that their ads do not show up on sites that may be inconsistent with their brand values, risk damaging their reputation, or simply do not perform well in terms of engagement or conversions. This functionality is crucial in maintaining control over where ads are displayed, thus helping to safeguard brand integrity and optimize advertising strategies.

The other options do not accurately describe the primary function of a publisher block list. Increasing ad visibility pertains to strategies aimed at enhancing the perception or reach of ads, and adjusting audience interests relates to targeting parameters rather than placement restrictions. Enhancing campaign flexibility speaks to the adaptability of a campaign in general terms but does not pertain specifically to the block list's role in negating unwanted ad placements.