Consider a scenario where a user visits a publisher’s website to read an article. If the publisher has sold its ad-display space to Google, Google will then access the user’s 3rd-party cookies to retrieve the user’s UID (Unique Identifier). This allows Google to match the user with its online database, analyzing the user’s preferences and other data collected from previous website visits.
Using this private information, Google can then align the user with advertisers who are targeting specific user segments. This segmentation, based on privacy data collected from third-party cookies, greatly enhances the value of the advertisement.
Ultimately, it’s the revenue from these ads that sustains the free internet.I think it’s quite remarkable.
data-empowered ad targeting, based on privacy data collected from 3rd party cookies. first party data collected by the advertiser can also be integrated and used for ad targeting.
further reading
How Google uses Customer Match data