How To Hide My Google+ Profile

When you add him in your list, if you only see the mail icon this mean your contact don't have Google+.

By the way if you click on the icon of a contact without an account, it will invite you to share by email or send (eventually) an invite.

In composing and editing the question, I might have come up with the answer myself:

• "Public" doesn't broadcast my post as widely as "Extended Circles" does. Yes, it's available but only to those who actively come looking.
• "Extended Circles" broadcasts my post not only to my circles but also to theirs. This gives me more visibility. But strangers can't see the post even if they come looking, unless they happen to be only semi-strangers because they are in the "extended circles".

So "Public" provides availability while "Extended circles" provides distribution. These are separate traits.

Frankly though, why would I write something that semi-strangers may read, but total strangers may not? That is what the "Extended circles" does, and it doesn't make much sense to me. So in essence, I would always use both in combination.