Ok, it doesn't do anything in a Rich Text field.
^ this is what I am referring to.
The default value does display initially, however if the content of the rich text TV (in the resource) is changed, and then the "Set to default" button is pressed, the content in the TV is not restored to what was defined as the default value.
To re-iterate...If the content in the rich text TV (in the resource) is cleared, and the page refreshed, it does repopulate with the default value, however if the content in the rich text TV is changed (you make it bold, for example), and then want to restore the TV content to the default value, the button does not work. Clearing the content and refreshing will do the trick, however that is only a workaround to what I believe is a bug. Also a client with no-development experience would perceive this feature as "not working", unless specifically instructed to use the clear-and-refresh workaround for rich text TVs.
Can you confirm this behavior? If so, I believe it is a bug, and will submit it as so on github.
If you can confirm my finding with TinyMce, do you experience the same thing using redactor, or does the "set to default" button with the redactor editor work as expected? I do not have redactor to test this case.