White balance allows you to adjust the color of lighting in the photo. The temp slider adjusts how blue or yellow the lighting is in a photo. The tint slider adjusts the amount of green and pink in a photo. These sliders are very useful for correcting or enhancing light in a photo.
Maybe you are inside and take a photo that has a yellow cast to it. Using the temp slider you can increase the blue and this will neutralize the yellow cast making it look more natural. Additionally you can use white balance sliders to enhance a photo. For instance if you take a photo at sunset. The camera isn't always able to capture the full spectrum of light. By increasing the yellow and pink sliders you can bring back the missing color detail of the photo.