Most of the professional photographers make sure, white’s stay white. Often we are challenged with tricky lighting conditions which make deciding on a white balance difficult. JPEG shooters are more vulnerable since the scope for colour correction is limited in post-production.
However, even if you’re a RAW shooter it is important to get WB close to perfect right in the camera. A bride on her wedding day looking resplendent in her saree would be disappointed if you supply her with photographs wherein her saree colour is way off. It happens quite a lot in wedding photography, purples turn into blue. Since the amateur photographer is lost in other aspects(composition, lighting etc) of the photograph, it(WB) gets easily hood-winked. However, the bride and her family are the first to spot the mistake. In rare cases, they might not complain but you are sure to lose the client for a future photo assignment.
In order to avoid such an unpleasant scenario, one should be careful about the WB during shooting. Often WB is a subjective topic. Some like their pictures to be warmer whereas others opt for the most neutral colours. I fall in the latter category. I do tweak the WB to one other than the prefect when I feel the need for it. Often I proceed with setting the camera’s white balance to a ‘preset’ closer to the lighting condition I am shooting in. When I shoot under mixed lighting conditions, I make sure to get a “Grey Card” reading from my subject. Of-course, I always shoot in RAW. Combination of these two methods give me a head-start when I have the photographs over the computer post shoot. Most often, the WB is spot on or close enough. The little adjustment(if required) is easily handled in post-production.