Why does the LED display turn off while the sleep timer is active?

The LED display will turn off after 10 seconds of inactivity when the sleep timer is on — this is a power saving feature and avoids light interference at night. Press any button other than the Standby ON/OFF to reactivate the display. Do not press the Standby ON/OFF button, as this will turn the machine and the sleep timer off. (Page 8)