No there is no law, but when someone comes on and asks about something specific, it seems as though they have their mind made up as to what they want. I tried to swap to flats and boots for the winter, and it was horrible. Boots are too bulky for me to get a good proper spot on the pedal, and I was using some huge wide pinned flats. After riding SPD's for so long, I am very used to them and the proper foot position that they offer.