No build step. That’s the advantage.
This appears to be a static site generator in that regard. Just that it outputs a single-paged app as opposed to a linked directory.
This isn't 'generating static pages'. It's rendering a page every time you access it, you've just moved the rendering to the browser's JS runtime.
It's better to spend just a couple minutes setting up a static site generator into your workflow than to have every user who pulls up your STATIC website perform template rendering and all that garbage. I know computers are fast and it doesn't seem like it really makes that much of a difference, but thinking like this often leads to inefficiencies in other applications as well.