When you just want to manage the post thumbnail or featured images, you don’t have that on quick edit option. You have to go to the edit page, change featured image, save and then go to another post edit page and repeat the process.
Now with this plugin, you can do that directly from your “All Posts” page. When you activate the plugin, a new column called thumbnail is added there. From there, you can add, change or remove featured images of your post.