In certain situations where a provider leases servers for other entities, it is desirable for the provider to be able to take back or reclaim the server. The superroot user is a separate user account made available only to the provider to allow the necessary access to reclaim and re-provision a server.
Use case would be such that the provider creates a superroot user and the customer would use the typical default user or a different user provided to them for their operations, creating/deleting users (except for superroot) as desired.
NOTE: If you as the provider is going to have the customer use the default iDRAC credentials, you would have to make sure the default credential warning and/or force change password are enabled if desired.
NOTE: Any concerns between provider and end-user relating to the superroot user should be addressed with a contractual solution rather than a forced technical solution.