Site Retargeting has emerged as a very effective way to put your message in front of consumers who have already shown an interest in your product or service. On average, only 2% of site visitors convert on their first visit to a website. Site retargeting is a tool to improve your conversions.
The key point here is that you are not reaching new customers but are marketing to customers that have been to your site previously but who failed to convert. When a potential customer arrives to your site, they are tracked by a cookie before they leave. This cookie allows retargeting companies to bring the user back to your site after they've left by showing the user display ads while they navigate across other sites.