Lets an author keep private notes with a post.
Sometimes when writing a post, you may collect additional resources to build the post. Such as reference URLs, thoughts, additional topics, forum threads to post in, etc. With this you can keep that info with the post, but it remains hidden to users.
Your notes will not be lost, but they will be publicly visible and seen the same as they're in your post, example: [note] my notes [/note]