If a client is able to offer better tools for low-level maintenance of disks (e.g., newer versions of fsck) when compared to the server, provision of NBD access seems sensible.
A scenario where the client might need extended network disk space for which a conventional network file system might not be sufficient.
An instance where the server may not have the ability to support the data structure or file system on the device intended for exporting.
During certain conditions where the application of NBDs may bring better performance as opposed to implementing conventional network file systems.
