They're dumb, but in a fun way. I created my own preroll video with some music and a silly title card. For me it's a fun way of celebrating the work I put into my setup (again – I use a very dumb video), but also Plex's preroll logic alludes me. It doesn't run all the time.

Mostly, however, I have trailers play ahead of my movie. It's a good way of remembering what else is on my server.

edit: also why, for the love of god, does Plex not pre-buffer the movie during either pre-roll or trailers? It makes no sense!