Found it’s very hit or miss for me. Many, particularly older movies (80s and 90s and older), are just the cropped poster and some seem like weird options that you have to wonder if they are for the right movie.
Deadpool 2 is using the “once upon a deadpool” artwork with Fred Savage for example.
Most seem to be the promotional artwork used on the poster simply reformatted for landscape (or as I said, just the poster cropped randomly to fit) and personally I don’t like that because I want the poster and the background to be different. And the cropping looking like crap is no good.
TMDB and TVDB handled that better. I’m really not that picky about the backgrounds, but I’m definitely having to fix backgrounds more often than posters now (and having to go back and fix the “defaults” being made worse) and that’s more time consuming. Luckily, still the ones I manually selected or set are staying put but because TMDB\TVDB did a decent job I often left them at defaults so… just a bit annoying to go back to fix now.
Edit: there’s also not an easy way to “scan” through backgrounds other than creating a new row on a hub or using PlexDash to see them one at a time (can set PlexDash to browse artwork by background but it’s still just swiping past all of the movies in single images).