When set to auto white balance, the camera attempts to detect and then correct any colour shift in the lighting. It's not always successful, though, which is why cameras come with white balance presets such as 'daylight', 'cloudy', 'fluorescent' and so on. Here, the colour correction is fixed for these specific conditions, and although selecting the right preset is more trouble, the results are both more accurate and more predictable.
Sometimes, you don't want the camera to attempt to 'correct' the colour of the light at all because it's actually an integral part of the photograph. Here, for example, the colour of the light is very different at two different times of day, but it's a characteristic that you want to preserve, not eradicate. The best solution here is to use the 'daylight' white balance preset because this will reproduce colours exactly as they are and not attempt any correction.
On most cameras it's also possible to calibrate the white balance manually, using a white card or some other colourless object to take a reading from.
So while it's tempting to set the camera to 'auto' white balance and forget about it, this isn't always the best choice:
• The camera may not correct fully for some types of artificial light
• It may correct lighting which shouldn't be corrected
