Sites running Paid Memberships Pro use it to:
Manage professional organizations with thousands of members.
Get paid for e-learning and digital courseware.
Accept recurring payment for content, podcasts, video, and more.
Create private social communities for unique interest groups.
Develop robust directory or listings sites by topic or region.
Offer product subscriptions or members-only product discounts.
90,000+ active installs.
Recommended by businesses of all types.
Paid Memberships Pro is the easiest membership tool for WordPress if you want to start taking payments immediately with little hassle. Setup is quick and the documentation is thorough when required, but I have not found much outside of the available add-ons that I need.