What is white balance?
Google describes it as the color balance on a digital camera.
Let's try to rephrase that.
If you take a photo and the image is orange, it's the white balance. If the image is purple, yellow, pink, or anything but your intended color, it's most likely the white balance.
Most camera menus use the light bulb (incandescent), sideways light (fluorescent), sun (direct light), lightning bolt (flash), cloud (cloudy), and house with slanted lines (shade). Oh, and let's not forget the custom and Kelvin (K) settings.
Personally, I go with AWB in most situations; more about that in a sec.
If you're not shooting in RAW, you should.
Because it makes correcting the white balance in post easier. Correcting a JPEG file could go from doable to almost impossible.
So what do you do?
You could either discard it or make it black and white.
Now back to AWB.
In the photo attached to this post, I left the white balance on auto. The camera chose what it thought was best for the situation, and I didn't argue. I think the purple tint on their skin helped convey the mood of the setting. Also, the lights changed continuously, and I didn't have time to switch between white balance settings.
Was I being lazy?
Maybe, but it worked.
Work smart, not hard.
Another reason to try AWB is that we, as photographers, sometimes forget to switch between settings. Think about this: you're outside where it's cloudy, only to come inside with the same WB settings. Before you realize it, you have taken 50+ shots, all with the incorrect white balance. Now you're desperately trying to save them in Photoshop.
Don't get me wrong. I do use the other settings when the situation calls for it, but you have to know what the lighting situation is before hand and prepare for it. If you use AWB, you can always reset the color in post. Shooting in RAW will reduce the possible undesirable effects. As your skill improves, switch over to manual white balance, even to kelvin. The difference will amaze you.