When writing an article, it's easy to digress from your main points by explaining them in more detail. You want to make sure your argument is solidly presented, so naturally you want to make a strong case. Or maybe you just want a footnote to attribute a quote of someone else's work (actually a topic of much discussion in the journalism world these days). A web page isn't the same as a sheet of paper, and footnotes at the bottom of the page create navigation work. Reading should not be work, so we've implemented a different way to annotate notes - we let you select a section of a sentence (or the whole sentence), and add a numbered note. The note is only visible when a reader hovers over it by moving the cursor. The reader gets to stay in the flow of the post, or can easily check out the side comment.

Try doing that on one of those social networks.