Org friends are a collection of people who’ve been added to your Blissbook account (usually because they’ve been granted access to something), who are not members of your organization.
The main use case for the org friend list is if you have multiple people with access to multiple documents, and you want to revoke their access from everything all at once. You can archive that person on your org friends page, and it will revoke their access from everything. This way you don't have to go into the audience for each individual document.
Adding someone as an org friend doesn't do anything in itself.