The entire point is that it will extract the embedded subtitles ahead of time (when the media is added to the library) so Jellyfin doesn’t have to do it when you want to watch it.
If it's a async process that runs on import/update of the library, that sounds great. I'm guessing we're/you're talking about Bazarr then? Although I don't see it explicitly mentioned in this thread earlier. Or some other application?
You can use this and then block embedded subtitles on a per-library basis, which is what I vaguely described a couple of posts up.
I agree this should be easier to find and set up.