The most powerful and cost-effective means of digital advertising. And it does not cost a thing to build. Consider the same principle as a contact list on your device. You create it, name it, and add to it. Then use it to plan and invite your market to your door.  This data is now shared over OTT, Ad Display, and Keywords and tagged for use in other digital tactics. 

With a small piece of text, a campaign will log a device to a retargeting list. Advanced Targeting can have higher costs. After the first interaction, the device will be logged into a re-targeting list. Using this list within a campaign, at a much lower cost, will identify and push advertising to sites the device accesses.  

Too much of a good thing may not be the best solution. Conditions can be set to stop re-targeting on a date cycle or after a purchase to avoid over-advertising. This is where your ad goes blind.  

If you have a provider which does not have re-targeting as a standard default; find one that does. This feature will only lower costs. The use of re-targeting is limitless.