This seems like bad advice, password auth is less secure than key auth^. And many servers don't accept password-based auth at all.
^password is sent to the server directly; passwords are generally weak and easy to brute force. Pubkeys without a passphrase _can_ be stolen from the local machine, but if an attacker has access to your local machine, you are probably SOL anyway.
edit: as several people have pointed out, this config option does not completely prevent pubkey auth being used (i.e. if configured or overriden on the command line). But if you only use that config by itself, it will disable pubkey authentication for every host.
^password is sent to the server directly; passwords are generally weak and easy to brute force. Pubkeys without a passphrase _can_ be stolen from the local machine, but if an attacker has access to your local machine, you are probably SOL anyway.
edit: as several people have pointed out, this config option does not completely prevent pubkey auth being used (i.e. if configured or overriden on the command line). But if you only use that config by itself, it will disable pubkey authentication for every host.