This feature is useful to allow device plugins to create fully customized objects using autodiscovery feature. The object can come with the right mapping in Data sources/Actions or you can even change its representation (eg: a light with a custom icon).
To test it
<name>My Test Template</name>
In Jfrontend enter Objects Edit mode and you should see a new template in the list called My Test Template which is provided by a device plugin instead of an object plugin.
Try to add it to the map as usual and check if this new light turns on when clicked.