Extended Circles The people in your circles (blue) can see your post in their stream if they have you circled. If they do not have you circled, they need to go to your profile to see the post. The people in your circles also have people in their circles...those people can also see your post but only if they go to your profile (unless they have you circled and then the post will show in their stream) Everyone else on G+ cannot see the post whether or not they go to your profile.
This assumes no shares to extended circles...which creates another hive of people who can see your post. Get it?