[giordano]

If the histogram isall bunched up towards the left but doesn't actually hit the left margin, it means you had a subject with a narrow range from darkest to brightest. In that situation even a digital camera has plenty of latitude. In film terms you'd have had a thin but perfectly usable negative. Giving a bit more exposure would have moved the histogram to the right and slightly reduced the amount of noise, but no more.

If the histogram is "cut off" at the left it means you have significant areas of the image that have exposed as deep shadow with no detail. In a low-range scene that definitely means you should have given more exposure.