My choice is dictated purely by subject matter and the impression I want to convey. I suppose my basic 'cut-off' point is that the type of images I would have seen in black and white while I was 'growing up' (as much as I have done) during the fifties and sixties still seem to me to work well in the same tones. When I decide to retain an image in colour, I often choose strong vibrant colours in PP, to enhance the effect, but for an image of muted, limited colour range, then i will do what I can to enhance that in my view. If people like my approach, then that is fine.