retargeting happens like this. You visit a website, say a travel booking site, and look at a page for buying a flight to Hawaii. You chicken out at the last minute, don’t buy, and navigate away, but the site has dropped a cookie for that Hawaii flight page on your browser. Then, when you visit other sites or social networks that run retargeted ads, they detect that cookie, and the travel site can show you an ad saying “It’s cold in SF. Wouldn’t a vacation to Hawaii be nice?” to try to get you to pull the trigger and buy the flight it knows you were already interested in.
But without cookies on mobile, you can’t retarget there…
…unless you can tie the identity of a mobile user to what they do on the computer. And Twitter can. It’s one of the few hugely popular services that individuals access from multiple types of devices.