Well, I actually don’t know but to me it seems like it’s optional if the value corresponds to what you actually want to have shown.
In my example “honey” shows up like that even though I wrote nothing in the content of the element. While if I do write something then the content replaces what is shown. It could be handy if in the value you want to register you don’t want to take capitalization into account but actually want “Ketchup” to show up.
Not sure if that’s how it is for you or for others, but it might also be browser related? I’m using firefox.