Another reason for a simple crush of the pepper on something like steak au poivre is the texture and mouth feel of the larger, coarser pieces of pepper. Instead of a smooth overall feeling when you bite into the meat, you actually bite into the pieces of pepper. Often you use different types of pepper, and with one bite you might bite into a black pepper bit, another a white or rose one, giving a little bit of different flavor in different bites. It's sort of like the difference between when you just flour something before sauteeing, or if you use dry bread crumbs, or fresh bread crumbs, or panko. All are basically the same ingredient, but give a different feeling when you take a bite.