Just a general rule about security.
Running any software with full Admin rights should be avoided in general. Only software which doesn’t work without these rights should get them. And then it should be used with caution or be specifically hardened.
Simply because any software can contain bugs, which could be exploited. If the attacked software doesn’t run with full rights, this can contain the damage an attacker can do.
This is basically what made Windows XP so much more safer than Windows 98. (and any UNIX-based system much earlier already)
Plex server doesn’t need admin privileges, so you shouldn’t grant them frivolously.
