This feature is specifically designed for two use cases:
1) Creating a toc for people that cannot easily do so using the conversion options (which are fairly complex/technical)
2) Quick touchups for books that have incomplete/broken ToCs.
Just a note of caution, this is completely new code, so there may be bugs.
Also I will be adding some new features in the coming weeks (like auto-generating the toc from headings or links and so on).