An Offline Root CA is a special deployment model that involves additional manual operational effort. It is kept in a highly protected environment and activated only in exceptional cases, for example when additional Sub CAs need to be created or signed. Such operations are typically required only infrequently.
The key advantage of an Offline Root CA is the high level of protection against unauthorized access because it is not permanently available during normal operations.
An Offline Root CA is therefore particularly appropriate when very high IT security requirements apply, for example due to regulatory requirements or particularly high protection needs.