I haven't bothered with torrents since we cancelled all our streaming services. Usenet is so good right now. SABNZBD, Sonarr, Radarr, Plex, Overseerr for my family requests/Plex share users. Finding a few good providers/indexers was really cheap (Black Friday sales were great last year).
It definitely takes a lot of fucking around/learning initially, but once you've set it up right, it's seamless.
Somewhat related - I hear real-debrid is a pretty slick way to basically stream torrents, if you don't have access to a bunch of physical storage. Haven't tried it myself, but people seem to dig it.
Depends on the setup. Maybe you run everything off a raspberry pi and can't afford to transcode 4k, so you have a separate 4k library for local users only. I could also see wanting to separate the volumes when you have multiple servers attached to a single NAS.
IDK, I don't personally bother with 4k, but I imagine it's a little more to manage if you're sharing your media out with friends/family.