Biggest upside of Plex for me is the fact that you can set up secure streaming from anywhere with basically a single click. With Jellyfin, that is much more manual. Besides that, I think some people may like that Plex has its own set of TV Shows & movies to stream, though I’m certain that those are ad supported. (Haven’t used that feature & have moved to Jellyfin)
Every time I’ve gotten an Amber Alert on my phone, the phone screams the description of the kid & the suspected car & possibly the suspect themselves on top of showing the entire message on the screen. No idea why anywhere would put all of that info onto Twitter only when this system already exists & really grabs your attention.