from the ssh_config man page:
If set to “yes”, passphrase/password querying will be disabled. In
addition, the ServerAliveInterval option will be set to 300 seconds
by default. This option is useful in scripts and other batch jobs
where no user is present to supply the password, and where it is
desirable to detect a broken network swiftly. The argument must be
“yes” or “no”. The default is “no”.