As an advertising and editorial photographer in Los Angeles, I usually shoot in RAW so while I always do a white balance before I start shooting. It is basic best practices even if it is not really baked into the image file. It is even more important when one shoots video which has a baked in color balance. Unless you are shooting one of the 4:4:4 video cameras which records all of the color information in the image file you are interpolating down much of the color information to a small percentage of the original. You cannot be far off in your exposure or color balance without downgrading your image in post corrections.
Yet, so often I have to remind photographers who are starting to shoot video that right after getting the exposure setting to white balance the camera. I would say this is important all the time rather than relying on the presets even if you are shooting daylight or professional lights. Very seldom do you really shoot in direct sunlight so there can be a bias in the diffusion material or fill reflectors. Lights get old and change color plus any diffusion can again cause a color shift.
I always carry a 12 inch Lastolite EzyBlance Calibration Card with me. It folds down into a 7inch carry bag and flexes out to 12 inch with a neutral median grey side and neutral white reverse side. The median grey side allows for both setting exposure and white balance. This can be especially helpful to wedding shooters that have to contend with white gowns and black tuxedos under mixed light sources.
Go to http://www.lastolite.com/ezybalance.php for more inforamtion.
Another handy device is the SyderCube. For RAW shooters you can use it alone to find your color balance. For video you can use it in tandem with the Lastolite EzyBlance Calibration Card to further refine your color balance. It has four areas for adjusting your color and exposure – white, median grey, black and black trap. Again, small enough to easy carry with you. Simple shoot the SyderCube and use the white and median grey sides with the eyedroppers and the black slider in Final Cut Pro to show a slight difference in the black and black trap. I’ll post a video using the SyderCube for corrections soon.
Go to http://spyder.datacolor.com/portfolio-view/spyder-cube/ for more information.