It's not wasted, it did something.
Zoro was not aware that it can do that, and had no control, that's why the result was unexpected. With knowledge and control, Enma will allow Zoro to use much more of his Haki to enhance his attacks.
Zoro was not aware that it can do that, and had no control, that's why the result was unexpected. With knowledge and control, Enma will allow Zoro to use much more of his Haki to enhance his attacks.
It is more Zoro will allow the sword to draw much more haki than the other way round which is why Zoro is holding it back currently