Post Tags Panel

If I click on Post Tags under the Posts panel, I can view a list of Post Tags that have been used, but I can also add new post tags.

The problem is the post tags I add in this fashion (which are attached to 0 posts) don’t appear in the list when I click on “Choose from the most used tags in Post Tags,” so it appears there is no benefit to adding a tag through this interface.

Is there any way to attach these post tags to an article other than retyping them? Is there any reason to add a tag though this interface? I can’t seem to see one, though the program allows you to do it.