I know what it does, what I was trying to say is, all champs have certain things that players need to learn about them to become "masters" at them. And his ult could have been an aspect of him that makes it harder for new players to do good on him, and make it more rewarding for people to learn and get good at him. In the sense that you would need to learn his damage and have a general understanding if it will kill or not, kind of like Darius dunk (I know its much different), in order to use it well. Ultimately, the indicator takes away that possibility for what ever reason Riot decided it should be there.
Personally, Cho is extremely easy, and as someone who like the idea of skill > kit, having no indicator would make him not as simple to just pick up and play.