When we sometimes (or often) has to capture a scene in a haste then it is not always possible to optimize the shooting settings. But as long as we shoot in RAW then we retain the possibility to optimize on-site shooting conditions at our desk back home.
Here is a good example. This photo was captured on the way home from a meeting today and while driving my car I noticed this sky with those nice cloud formations and colors. So I pulled the car of the road, rolled down the window and stabilized my camera on the door frame. I didn't have time to think much about the correct shooting settings, but just dialed in a suitable shutter speed and aperture value in Manual mode.
As you can see the white balance is wrong and the exposure is not correct. The corresponding histogram looks like this:
Clearly the exposure is distorted to the dark side and lacking more dynamic area in the middle tones.
After some tweeking in LR3 I came up with this photo. It is evident that the white balance has been corrected (using the White Balance Selector tool). The histogram also displays a much more balanced distribution between dark and light areas.