Help me understand permissions

Hi all, I've just bought a DXP4800 and am in the process of setting things up. I'm trying to get Plex running in a container via the guide from MariusHosting here. He has the user set up Portainer and Plex using the user account which I can only imagine will be full root/admin access in most cases. Is this safe? Would it be better to create some service accounts and use those for running services rather than the admin account for the whole NAS?
I'm new to Docker, but not to infosec and while the guides are clear in what to do, they don't really explain why you need to do whatever it is. It feels like this should be stated when you're having people ssh in and elevate privileges.