In Facebook, when user JohnDoe views a post which has been added (by JohnDoe or by one of JohnDoes friends) on JoeDoe's Timeline, what is the point of JohnDoe's user interface displaying both:
friends drop-down menuicon above the shared media (text/picture(s)/video(s)), just to the left of the poster's name and post time, allowing JohnDoe to control the visibility of the post (which can be set to Public, Friends, Only Me, a predefined Custom List or Smart List of friends, or any Custom list of friends).
Share buttonbelow the shared media, which allow the post to be shared with the very same group of people (and thus seems as though it achieves the same thing).
What I could gather is that, by sharing, you are posting the same thing to your timeline one more time, perhaps at a later date. I don't understand the need for duplicating the post on one's timeline in this manner, seems a bit like spamming to me. Perhaps someone can explain.
NOTE: I've also noticed that the share button I mentioned also allows you to share a timeline post to someone as a private message, functionality which the friends drop-down menu of a post doesn't allow you to achieve. Perhaps this is one of the differences that could be pointed out.