Exposure compensation in manual mode doesn't change anything about the image, but it might be useful as a "guideline." Say you're shooting pictures in a snowy environment. If you "match the needle"--i.e., set the manual exposure so that the blinking icon is at "0," the images will be too dark and the snow will look grey. That's because the camera is set to make a grey (about 18% grey) target look correct. When it sees a lot of white, it will tend to underexpose. You can deal with that in manual mode two ways. First, you can leave exposure compensation at 0 and ensure that the blinking icon is at about +2. Second, you can set exposure compensation to +2 and set the blinking icon at 0. The results would be the same, but one method might be more convenient for you. Setting the exposure compensation might be a good way to "remember" to push up the exposure. On the other hand, if you move to another scene, you should remember to reset the exposure compensation.