I do (post private) before this notification, now my case:
* We are a team of 12 members
* Only 3 members made publications (one editor an 2 admin)
* We have a list of 200 or more potentials followers
* We need share some post with the group but not with followers
I need difuse the public post to followers, share some post with somme membres of one team (without wordpress.com account), and have private post for share with the only 3 membres that have an account sur wordpress.com
I do the report for made better wordpress becouse it have potential but i find many many bugs (in logic and in software) and I try to send feedback.
I think that followers are followers (mail, twitter, facebook) and is "stupid" made a massive diffusion of a non public post, because you have to send a mail with the password in private.
In the other hand, if you are the follower, is not nice get a mail with a post thath others can see and you can't (becouse is not for you).
One solution is a configuration option for decide it, becouse for others can be good idea send the pasword protected post to followers.