Advertising cookies exist to connect a person to something they did somewhere else: an impression, a click, a purchase. They are the category with the most parties involved, the most data leaving your site, and the least visibility for the person who owns the banner, because the tag that sets them was usually installed by somebody running a campaign rather than by whoever maintains the code.
What actually happens when one fires
A script from an advertising platform loads in your page, writes or reads an identifier, and sends a request carrying that identifier plus context about the page. From that point the platform knows this browser visited this page on your site, and can use it to target or to attribute. The data has left. Nothing you do afterwards recalls it, which is why the gate has to be before the tag rather than around it.
Why this is where the exposure is
Regulators act on advertising storage set without consent more than on anything else, because the harm is easy to articulate and the evidence is a single page load. It is also the category where the disclosure is hardest to keep accurate, since campaigns come and go and each one may bring a new pixel. A quarterly comparison of the live tag list against the banner's advertising category catches almost every drift.
Getting it right without losing the campaign
Gating the advertising tags does reduce measured conversions, and that is a real cost to weigh rather than one to hide. The mitigations worth having are consent mode where your platform supports it, so the platform can model the gap rather than see nothing, and a clear internal note about when the gating shipped so the drop is read as expected rather than as a fault.
Questions people ask about advertising cookies
Do I need advertising cookies for retargeting?
In the classic form yes, which is why retargeting audiences shrink when a banner starts working. Some platforms now offer modelled alternatives.
Is an advertising pixel a cookie?
The pixel is the request; the cookie is what it sets or reads. Both are in scope, because the rule covers storing and accessing.
Can I put advertising under functional?
No. It is the clearest case of a category that needs its own consent, and misfiling it is an obvious finding.