Subscribe component is used for:
1) To sell individual article to individual user by paypal payment processor.
2)To sell digital products to individual user by paypal payment processor.
3)To make a digital product 100% secure so only user who have permission to download the file can download it.
4)Free product and free article can also be created.
5)In subscription you can set time in months/years/days for product subscription expiration.
Compatibility : Joomla 1.5