If I mark a post to be viewable by public, does it mean it is viewable to all my circles? Or should I add the post to my other circles even after marking it as public?
Public posts on your Google+ stream are visible to:
- all users in your circles
- other users you have never interacted with
- anonymous users who don't even have accounts
When you post publicly, people who've added you to one of their circles will see your update on their Home page. Your public posts will be displayed on the Posts tab of your profile and are viewable by anyone who wishes to see them. They also may appear in search results.
It is not necessary to add people to circles if you want them to see posts marked "Public".
Public posts are just that - public. Anyone who has you in a circle that is visible in their stream will see it in their stream, and anyone who looks at your profile will be able to see it directly.
People often add additional circles, or individuals, to the post destination to (hopefully) trigger a notification for that person. This notification is via email and/or the red notification box. This is not guaranteed to work, however, since Google+ imposes a limit on how many notifications can be sent from one message, and the individual receiving a message may have muted you.