I recently discovered on the forum that I could set samba aux paramaters as follows to disable NetBIOS:
disable netbios = yes smb ports = 445
If I correctly understand https://en.wikipedia.org/wiki/Server_Message_Block#Features then it seems that NetBIOS support is not needed if all computers are running Windows Vista or newer.
Disabling NetBIOS reduces the attack surface of one's FreeNAS server, because an entire port is closed.
Therefore, it would be nice to have a GUI method to disable NetBIOS. (I'd also argue it should be disabled by default.)