Why does the Minecraft Wiki fail to leave the server ip empty?
Where did you get that? If this is a contribution, please post the link.
Okay, it's about the server.properties
If you leave the server-ip blank, the server will "bind" all IPs.
(Technically this would be '::' for all IPv4 & IPv6 addresses)
These are the IPs over which the server will accept connections. (incoming)
If you leave it empty, the server can easily be copied to another machine and you don't have to adjust the IP.