This feature is used to allow device plugins to create fully customized objects using auto discovery 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
Create a src/main/resources/data/templates folder inside a device plugin (eg: essential)
Copy the light.xobj object from base-things plugin in this new folder
Change the name of this file to mytemplate.xobj and change xml name
<name>My Test Template</name>
Recompile essential plugin to have these changes installed in freedomotic-core
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 the new light turns on when clicked.