Every camera setting is subjective, including white balance. Some of the top wedding photographers use auto white balance. Some do custom white balance for every shoot. I used to believe in auto white balance for everything. For the most part, situations are always changing and therefore white balance is always different, so auto helps.
But since color temperatures change, so does auto white balance, meaning every image you take could have a slightly different white balance because of what the camera sees, even if the real white balance is fairly consistent. For example, under the sun, the white balance is the same no matter where you go, but the camera could see it differently and make slight adjustments. So you could needlessly be correcting white balance all over the place when a single setting — Daylight, for example — would have been much better.
Remember, when shooting RAW you have unlimited flexibility for adjusting WB in post. So if you pick a consistent setting, like Daylight or Shade, you’ll at least have a more consistent starting point in post. If you do a custom WB for every lighting condition, you’ll be in an even better starting place, but it’s more work. If you take a shot of a known white target — I recommend the ColorChecker Passport — for every scene, you can get perfect WB in post with just a click. It depends on how particular you want to be and what workflow you like.
One thing about getting WB correct in camera — it doesn’t matter in post if you’re shooting RAW, but it means you’ll get a better image when reviewing the LCD, since the LCD image is a JPEG created from the RAW settings in the camera. RAW files themselves have no white balance or color space.
The ColorChecker eliminates guessing and inaccuracies by providing a known white point for the scene that you can quickly select on the spot or in Lightroom. I can use the white card to create a custom white balance in the camera before I shoot, ensuring consistent results that are easy to correct if necessary, and an accurate review on the LCD.
The ColorChecker also enables you to create custom color profiles for different lighting conditions. This is different from white balance in that it corrects color for the spectrum of light, not the temperature of the light. The color profile returns colors to their truest hues, and this is something not possible without a system like the ColorChecker. Without it, you’re using generic profiles to tell the software where to place color, which doesn’t provide rich or accurate color, even if it looks like it does. Until you see a comparison of generic profiles to ColorChecker profiles, you really have no idea what you’re missing, and it’s a lot.
So for me it will be no more auto white balance for everything. In some instances it will be necessary, such as weddings, when things are moving too quickly to think about WB, but when possible I always like to have a consistent WB setting.
If you’re shooting JPEG, you have almost no flexibility to adjust WB after the fact, so you must be as accurate with WB as possible in the camera if you want any hope of getting accurate color. In this case, matching the camera’s WB setting to the temperature of the light you’re in, or doing a custom WB with a white card, yields more consistent results than auto WB.