There are two use cases of TOC's that would be useful.
Child Pages (like Ian's comment)
You can see the child pages in the side navigation however, If you have the child pages listed in the current page you can then the sub-pages are visible when you share just the page or when you have a loop component of a page (or part of).
Sections/Headings
Have a TOC component that you can add anywhere in a page that will inline links to the sections in the page. This enables better navigation for long/large pages. Would want it to be available when viewing a shared page and in Loop components.
The intent is to be able to have a "unit" for a page, it's content sections and it's sub-pages - that travel with the page.
Where can I vote for these improvments. I would love to have them.