d4 Exposure Delay Mode
Explanation: Exposure delay mode means that there is a delay of about one second between flipping up the internal mirror and the beginning of the actual exposure.
This prevents shaking of the camera body because of the mirror movement during the exposure.
Recommendation: The usage of this feature is rare. If you take pictures with the camera on a tripod and the shooting situation is sensitive to camera shaking (i.e. macro or long tele lenses) and the exposure time is in a certain range of about 1/60 to 1 second it can bring you better sharpness.
But you do nothing wrong if you switch it on whenever the camera is on a tripod, that‘s what I do.