Contriving color information from any single-chip sensor inherently creates a compromised image that's noisier, fuzzier and lower in resolution - but waiting beneath the filter that splits every other pixel into RGB, there's a pristine, full-resolution monochrome frame. It would be a incredible if we could access it when shooting in B&W is required, and then reset the bayer filter when we need to return to color.
Besides, all else being equal, movies always look better in B&W
Besides, all else being equal, movies always look better in B&W