Why whole peppercorns? Some recipes call for whole peppercorns. Why not crack them and use a lot less? In a cooking show I watched recently the host specifically said "Do not crack or grind them" but he did not explain why.

The only reason I can think of is to make it easier to take them out of a sauce or soup if you want the taste of pepper but not the texture/appearance.
With whole peppercorns you will eventually bite into one, giving a burst of peppery goodness. This works only if the dish is to be cooked enough to soften the corns. I love to do this in soups and meatloafs. It could also work in casseroles.