The given configuration is an example which shown all available configuration options. There is no need to use value_template: if the payload matches the configuration thus marked as optional. value_template: is useful if you can't change the MQTT settings of your device.

Well, {{ value_json.x }} would maybe be the better sample for the payload but {{ value.x }} it's only a placeholder and if one follows the link the templating docs it should become clear.

There is no need to use value_template: if the payload matches the configuration thus marked as optional.

That's strange, because I did try removing that and it still didn't work. It only started working when I changed it to value_template: '{{ value }}'.

#597 will update the docs for the new cover component which combines garage door and roller shutter.