To me, the use case is really obvious: when you reached for SQLite but now want something with Moar Powah.

Now I've reduced it to a previously answered question: what's the use case for SQLite? ;) https://www.sqlite.org/whentouse.html

That being said, I don't see the point, and shudder at the idea of a web page's javascript doing anything which needs noticeable amounts of the CPU, but I'm a non-standard user...