Many photographer's struggle to visualise a scene in black and white, so this little trick can give you a hand.
Another great benefit (as mentioned above) of shooting RAW is that you can then safely set your 'Picture Style' to 'Monochrome' to have the camera display your images in black and white (a handy preview to help you visualise the scene in black and white), safe in the knowledge that all the colour information is still being saved by the RAW file for you to work with later. When you load the RAW file in an image processing program such as Lightroom (or similar) you'll see and have access to edit the full colour image. Many photographer's struggle to visualise a scene in black and white, so this little trick can give you a hand.