Originally posted by geomez The camera's metering is imperfect, and exposure compensation let's you correct a camera's bad metering if the results are too bright or too dark.
I would take that a step further, because I don't believe it paints an entirely accurate picture. As a camera is a machine, it has no idea what is in front of the lens. Depending on it to make decisions about exposure rather than making them yourself is inviting the camera to meter "inaccurately."
If you want to use auto metering modes, the way to get a consistently accurate readings would be to hold a gray card in front of the lens, read and lock the exposure, then shoot the image. I did this for the 9 years during which my K1000 was my only camera (which was from 2000 - 2009), and it never let me down. The trick is that you have to make sure to read the light that is the same light that is illuminating your subject.