The electronic paper display is always on, but in a less disturbing and more friendly way. You can easily see notices, emails, tweets, and other information in real time without picking up or even activating your phone.
The electronic paper display does not have to go dark to save battery life. Even if the battery dies, the most recent information on the EPD will remain visible. You can use it to save important information. Save anything from a route on a map, to a boarding pass, to theatre tickets.