I like writing as way of collecting my thoughts. Some of these thoughts are half private, half public. They are matters I like to share with a few choosen ones, but don't like to share with anyone else.
I find the password feature a lame solution to these cases. I want the posts to be invisible (not showing up in the blog at all) to readers who aren't entitled see them. And those who are entitled to see them, shouldn't have to write a password for every post.
It takes a new user role, a Private Reader role. A Private Reader (or whatever you'd call it) is someone who may log in, and thereby see both Published and Private posts (not Drafts). Or you could have a fourth Post Status for these "half public, half private" posts.
At first I thought the Subscriber role had this function, but as far as I can tell from the docs, its function is to let people in to see the Dashboard without letting them change anything. Why would anyone want that?