Another vote of "thanks" for a plugin that performs a very necessary task.
When setting up a Custom Post Type, I was cruising along selecting featured images for the posts. When I needed to remove the featured image, I did so on the Post page 'remove image'. But I discovered that, while the post page for the CPT showed the image removed, it nevertheless remained 'attached' and visible in my posts.
Interesting that the featured image functionality works for CPTs to add the image, but not remove the image from being attached to the CPT.
I used Unattach, it worked, and the unwanted CPT images are now properly unattached. Thanks again.