But all the tasks in the article are totally straight-forward SSG stuff. Why would you do some processing in a build step, but then stop half-way and ship a bun

But all the tasks in the article are totally straight-forward SSG stuff. Why would you do some processing in a build step, but then stop half-way and ship a bunch of JS to the client so they can finish it? That only makes sense if the work is dynamic in some way that it can only be done on the client-side.