Any better grade desktop computer can be configured with a multi card reader but I have never found that a problem. I, almost without exception, download directly from the camera body. This eliminates the constant and recurrent removal process that risks damage to both card and internal pins. It also greatly reduces the ingress of dirt or other foreign matter to the camera body. Other than some gain in transfer speed, I doubt if one card is better than the other. Nikon pro digital bodies have always utilized the CD card and the SD was reserved for consumer level equipment. I suppose as far as Nikon was concerned, size did matter at the time. If I were to hazard a guess, I would imagine that the SD card as the second slot was for the same reason, grabbing some camera body real estate.