questions and thoughts about twitter

I’ve been using Twitter for sometime now. And I’ve always wondered about the settings in Twitter, especially one particular setting - “public vs private”. Let me first review the setting. If you set your privacy settings to “private”, then all posts after that time-line will only be available to the followers that you have allowed. And if at some point of time, you decide to toggle it to “public”, then all posts (even the ones you sent in the past - as private) becomes open to the public.