The concept
A membership area is where the digital product is actually delivered: lessons, PDFs, community, files. It exists to separate who has paid from who hasn't, and so that access doesn't depend on someone sending an email by hand.
When the area is integrated with the payment platform, the sale's approval triggers the creation of access within seconds, and cancellation or refund removes that access the same way. When it isn't integrated, someone has to do both things manually, and that's where most complaints about undelivered products come from.
Fast, verifiable delivery is also a defense against chargeback: the record that the buyer accessed the content is evidence in the dispute.
How it shows up in practice
You launch an infoproduct and need to deliver lessons, PDFs, and community only to those who paid. You set up a membership area, which is basically a logged-in space where only those with access can enter. Integration with the payment platform makes this work in seconds: sale approval triggers access creation, cancellation removes access.
Content is where I expect much of the real money will be made on the internet.
When this integration doesn't exist, someone has to unlock access manually, and that's where complaints of product not delivered are born. Plus, the record that the buyer accessed the content is your best defense against chargeback, proof that delivery actually happened.