It may not be a killer, but it would be helpful
In some ways, a smartwatch screen is the place to post scores of an ongoing game or display equities prices on a busy trading day. With a turn of the wrist, the wearer catches up on the information he needs with minimal interuption in the other thing he was doing. And of course the smart phone screen can serve the same purpose. It's just more disruption if your two hands are already busy.