Retargeting can be quite effective, along with other forms of first-party data used for targeting- such as CRM data to inform which ads are relevant. Behaviora

Retargeting can be quite effective, along with other forms of first-party data used for targeting- such as CRM data to inform which ads are relevant. Behavioral data using 3rd parties like Neustar / Lotame have more dubious results, but still rake in billions each year from ad buyers that fastidiously track their ROI. Most online display works to reinforce messaging in other forms of media, or win over new audiences with sheer volume.