Yeah, it's a massive "no no". I'll clear this up a bit more so people understand why this happens.
Since we're on the subject of Sonarr, I will use that in this simple example.
The service Sonarr runs on your dashboard. The process shows as active by checking that the process exist, either under the services name (example, Plex process runs under the user created by Plex, which is
plex) The Sonarr service checks that the Sonarr/nzbdrone processes are running as your username. So it will check as the following (you can find this in your /srv/rutorrent/home/inc/config.php file)
$sonarr = processExists("nzbdrone",$username);
When you run this service as username
plex for instance, what this does is it checks the processes as
$sonarr = processExists("nzbdrone",plex);
Sonarr is smart enough to know that's simply not right as another service requires this name to run. Thus it fails as it is struggling with the logic that another service is attempting to run it's processes. This could also cause conflict with it's initial installation.
It's a common misconception that one would need to make a user named
plex to have certain privileges for running Plex on your server. I would advise a new username to address this issue.