In the film days, I always found that I had a lot of difficulty shooting color and black and white simultaneously (with 2 cameras). I had to sort of get into the spirit of black and white. To some extent now, if I shoot in RAW and convert later, getting a good black and white is something of a fluke, not something I "intended." I'm thinking (maybe wrongly) that specifying monochrome in the camera (something some cameras can do -- one of mine can) which causes the digital image on the camera to be black and white helps me to look for good black and white subjects, even if when you get back to the computer, the black and white jpegs embedded with the raw get converted back to color. Course I can only do this if I set it to RAW + Jpeg so while the RAWs revert, the jpegs stay black and white.