It happens rarely for me, but sometimes it’s easier to shoot against green than lighting a white space. I recently was asked to shoot a very straight forward stand-up promo that required a white background. It was simple enough as this would normally be done against a white cyc. However, in this case, the studio was already painted chroma-key green and could not be painted white in time for the shoot. The director also wanted a somewhat wider shot, so rigging a large white fabric would have been really costly in time and materials. The simplest solution is often times the best; shoot it against green and key in white after in post.