By default, WordPress gives you one editable content area per page. The Other Content allows you to create additional content areas for some or all of your Pages or Posts. You can create as many additional content areas as you like, and call them whatever you want.

The Other Content

By default, WordPress gives you one editable content area per page. The Other Content allows you to create additional content areas for some or all of …

Didier Sampaolo

When you write a long post, it is common to add h2 and h3 tags to create sections on a specific topic. This plug-in will search these sections and add a link to each of them at the beginning of your post. Each section will become a named anchor, allowing the user to browse quickly through your post. 
This summary is also understood by major search engines and should improve your CTR (click-through rate) by providing richer snippets.
<a href="http://www.didcode.com/code/wp-summary.html" rel="nofollow ugc">Plugin home page</a>

wp_summary

wp_summary will automagically show a summary of your post at its beginning, using h1, h2 and h3 tags to create sections.

The Other Content vs wp_summary