The answer seems obvious: without white balance, we would have bad color reproduction, because different lighting would produce lots of different color tints. Our eyes adjust for the color tints so we can reconstruct the real colors of objects, so cameras need to adjust white balance too.
But that seems strange. We clearly can perceive color tint in scenes: everybody can see that incandescent lamps are yellowish, while fluorescent lamps are very white/slightly blue. But with auto white-balance, the color tint is removed in the photograph. Both incandescent lighting and fluorescent lighting become white.
And though our eyes do adjust to color tint, why don't they adjust when looking at a photograph? Why does the camera need to do work that the eyes would already do?
This seems to imply that to get accurate color reproduction - including color tint that we perceive and thus want to capture, just set the white-balance to daylight, all the time.
But white-balance evidently is necessary. Even in a room with terrible incandescent lights that give off a strongly perceptible yellow cast, the image on the digital viewfinder still looks much more correct with the white-balance on automatic, than with it on sunlight! I just stood there messing with the camera for quite a while, and I'm still really confused why this is the case. Why would the viewfinder in the room, which shows an image without yellow tint, look correct literally right next to objects illuminated with a strong yellow tint? And when I put the camera on sunlight, the screen suddenly shows a WAY stronger yellow tint than the actual room, even though my yellow-adjusted eyes should shift both the room and the screen back to white, no?
Is there something about screens and photographic paper that make our brains/eyes "turn off" our internal white-balance correction?