Earlier quoted context omitted.
Advertisers/ad networks need to serve ads from their own domains so that they can identify the visitor via 3rd-party cookies and serve the most appropriate ad.
> serve the most appropriate ad Is it just me, or is this approach not very useful? I'll google for a certain product, do a little bit of research and then buy what I finally picked. Then I'm stuck with seeing ads for similar products for the forseeable future. Ads for a product I already bought and no longer have an interest in. I think ads would actually do better if they're just targeted to the demographic that fi…
There's a gap: Getting search/retargeting interest information is almost instant, but finding out you've purchased is hard and takes time.
However it's effective enough: Retargeting boosts most verticals by as much as 3-5x, and where that one click pays $1 the ads cost about $3 per thousand to display them.