Here are things I'm currently using root for on LineageOS:
System-wide adblocking (hosts file with Adaway). Yes, there's DNS-based adblocking, but sometimes that can be slow or not play nice with public wifi networks.
Battery management. I use AccA to limit my battery capacity and charge rate to keep it from wearing out. I might not care as much if the battery was easy to replace.
File management, as there's an increasing amount of the filesystem blocked off without it.
Yes, it's my main back up app. (The latest update kinda broke it though, I think first time happening, but the issue was spotted and will be fixed.) The only big limitation (which might have been fixed actually) is backing up and restoring app on work profile (anything other than user0).
The benefit to longevity from limiting battery charge even a little bit is pretty substantial. I recommend it to most people with the technical ability to do it.
Fair, but I guess my point was I haven't personally needed those things in some time. At least, not enough to warrant exposing myself to vulnerability like before. Ad blocking especially, since you can do that via VPN or by using your VPN slot if you don't want to use something like pihole. App + data backups are built into many custom roms as well, including the one I use (graphene).
Everyone's security and convenience/feature needs are different of course. There is often a tradeoff. The way I see it, I wouldn't give up having admin access on my PC for security, so why would I give it up on my phone?