New visitors vs returning visitors, coming from paid or organic searches, via email or referrers, English, German or French speaking, and the list goes on.
When can you target them?
Target them after any number of minutes or page views spent on site.
How to convince them to subscribe?
Incentives work great to lure visitors to your email program.
PLUS
A/B testing of your targeting campaigns. Integration with major email service providers. Real time reporting.