When starting the server without "--log.file -" directly - i. e. not using launchctl - the output is log to the log in /usr/local/var/log/arangodb/arangodb.log.

That seems to confuse people, because the type "/usr/local/sbin/arangod" and see nothing at all (because everything goes into the log file). With the added option, the log is send to stdout instead.

You can start the server with or without the additional option. But the more sensible one seems the "log to stdout" one.