This photo was made when the flash units did not function and is about a 4-5 f-stop underexposure. It captured only about 3-6% of the available pixel information available in the camera. Notice the poor color quality and lack of details compared to the previous image.

This is an extreme example of what you loose when you underexpose a photo. So, always expose using the histogram to ensure the histogram curve comes very close to the right hand edge. Doing this will preserve the best image quality your camera has to offer.