White balance is the camera setting that corrects for a light source's colour temperature, so a white or neutral-grey object in the scene actually renders as white rather than tinted orange or blue.
White balance corrects for the colour of the light so that something neutral in the scene records as neutral rather than tinted. It matters because light sources vary more than the eye registers: household tungsten bulbs are strongly orange, deep shade under a blue sky is genuinely blue, and fluorescent tubes lean green. The brain compensates automatically while you stand there, but the file keeps whatever cast was present.
Getting it wrong is not a minor stylistic issue in genres where colour is the product. A plate of food shot under warm kitchen light without correction looks greasy and orange; a clothing shot under mixed lighting can misrepresent the actual colour a customer receives. Shooting raw lets white balance be reset later without quality loss, but fixing a bad in-camera setting still costs editing time, and two different light sources in one frame cannot be fully corrected with a single global adjustment.
A photographer shoots a product catalogue for a paint brand, where the exact colour of each sample has to match reality. Under the studio's LED panels set to a warm 3200K, leaving the camera on Auto white balance produces slightly different casts frame to frame as the composition changes, so a grey sample photographs faintly warm in one shot and faintly cool in the next.
Setting a fixed Kelvin value and shooting a grey card at the start of the session locks it down: every frame is corrected to the same neutral reference in editing, and the paint colours come out consistent across the whole catalogue. Auto white balance would have been fine for a lifestyle shot of the same paint on a wall, where mood matters more than an exact match.
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