Audience portability means the relationship is yours, not the platform's. On most social platforms it is not portable: you cannot export usable contact info for your followers. On hashtag.org, the people who follow your #Name and opt in are first-party data; you can message and migrate them anywhere, including off hashtag.org.
Creator economy & platform risk
Audience portability
The ability to take your followers/customers with you when you leave a platform.