This gives you a preview when you hover on the previous/next links in a single post page.
Using the functions provided by this plugin, when you hover on the previous/next links in a single post page, you can see a preview of the post.
It shows an excerpt of the post. The excerpt is generated using the same mechanism as "the_excerpt" tag. If there is an explicit excerpt for the post, the explicit excerpt will be used. If the post doesn't have one, an excerpt is faked by truncating the full content.
If a post is password-protected, no preview will generated for it.