You're basically asking about the difference between an authorized vs unauthorized biography.
If you sell the rights, that's just getting some nominal fee in exchange for your participation in the process. You may have insights and knowledge of certain events that aren't easy to find without your help, so some media production company may pay for you to fill in those gaps.
None of that is strictly necessary, though. Anyone can write about anyone else, so long as they aren't making false claims about the source, or making other negligently false claims of fact. (Don't do false advertising or libel.)