At least on Windows, Zabbix agent fails to start if Server= is commented out in the config and
StartAgents>0. It fails with error like this:
zabbix_agentd : ERROR: StartAgents is not 0, parameter "Server" must be defined
However, default comments in zabbix_agentd.conf says that this parameters is not mandatory. And there is no dependency on StartAgents documented.
Here how it looks like;
Please consider to change default, or document this situation more accurate.