We strongly recommend leaving PermitRootLogin enabled. Ploi connects to your server as the root user to provision software and run management tasks, so disabling root login over SSH cuts off Ploi's access and your server can no longer be managed from the panel.
If you have security concerns, note that Ploi already hardens root access: password authentication is disabled, so root login is only possible with the SSH key Ploi installed during provisioning — it is key-only, never password-based.
For your own day-to-day access, use the less-privileged ploi system user and leave the root login in place for Ploi.
