This is a very simple (but useful) plugin. All it does is:

1. adds a "Featured Image" checkbox to the Screen Options when viewing in All Posts mode.
2. when the checkbox is selected, it will add a thumbnail of the post's Featured Image to the All Posts screen.

This allows you to:

1. easily take an inventory of posts to see which are missing featured images (in this day and age, all posts should have a featured image) and
2. quickly scan your posts—it's frequently easier and quicker to identify a post by its featured image than by scanning titles.