When I know I'm travelling, I always download a few select movies and the next few episodes of whatever we're currently watching to my devices.
Plex allows me to download using my PlexPass. My family/everyone else that uses my server download the media they want via my JellyFin server (serving the same media as my Plex server).
I'm not a noobie to the high seas, but I've never had issues getting all of the new TV shows and movies we watch from public trackers.
What are the actual benefits to closed groups like these?