I recently had the duty to shoot overcast-outdoor-mixed-with-tungsten-and-candle-lit-low-light-indoor (quite a nightmare without flash) and I always had the D800 AWB on. I tested Lr on raw files to see how good was my choice. D800 AWB was doing a very good job … look at the paper in the hand of the girl in the post picture: it was white, not cyan, not yellow.
WB is quite an artistic choice, not a technical one. That said, there are different WB schools out there. Purists go for a fixed daylight WB. Warm-saturation lovers go for a fixed overcast WB. If you do not belong to any of them, you are probably very often satisfied with your AWB and you correct it in raw when needed.
There are many rumours around D800 bad quality AWB and suggestions agree on A2, M1 (or even A3, M2!). It’s a good solution to get better pictures on the LCD … and magenta overcast pictures on the card. So, I would not suggest doing such adjustment.
The Lr AWB gave a yellow cast on skin and car this time … not sure I will use it again.
A bad point for D800: there is a green/yellow cast on the LCD, it is not just “a better representation of reality” as Nikon likes to say. Have a calibrated monitor (Win7 monitor calibration works easy with me) to judge your work, don’t trust the LCD.
Conclusions? Set your WB on the colour memories of the event and on logical patterns if you have unexpected tones. Was that wonderful dress red or magenta ? What does the D800 flash WB say?
Also, choose the WB you like more or that is more suitable to the situation: better a suntanned bride or a pinky groom? Candle lights aside and outdoor light back: what is the priority for the atmosphere of this picture?