When this feature is enabled, a ProFTPd virtual server will be created for this Virtualmin virtual server. This can be used to set up an anonymous FTP site that is private to this server. However, it requires that the server have its IP address.

This feature is only needed if you want to provide name-based access to an anonymous FTP server. Almost no one needs this feature to be enabled (that probably means you). You do not need to enable this feature if you just want to provide FTP access for the domain owner account, as any user with a shell accou nt will automatically have FTP access to their home directory.

In other words: You almost certainly don't need this, even if you think maybe you do.