i think "unlisted" is probably the post setting most of us want to use for most of our posts, it prevents posts from showing up on either public timeline
(or "followers only" if you're a locked account and want your post accessible only to followers.)
Follow
locked accounts seem a little quirky over here. your posts can still be public if you're not paying attention - you need to make sure you have "followers only" selected if you want them to be followers only
