Blog_url in blog and item templates


In the Quark theme, in both the blog and item templates, the blog_url variable is set, supposedly to set a path to the blog, different from the one set at the theme level (in blueprints.yaml as blog-page). In the help of this variable I see the following: “The route to the main blog page that contains the “Show …” configuration”, which I don’t quite understand. What does that ‘Show…’ mean?

On the other hand, if I set in the Blog blog_url: /blog-1 and in that same blog, an item with `blog_url: /blog-2", all the sidebar plugins now point to the root of the server (http://localhost/archives_xxx or http://localhost/tag:tag1) instead of the page path (http://localhost/grav/archives_xxx or http://localhost/grav/tag:tag1) .

The question is: Is the blog_url variable in the item template necessary or useful?