I've always used Normal cycle on all my machines for the most part. Unless there's a horrendously filthy load that has accumulated over a few days. With the PowerClean I used it almost exclusively, the Voyager as well because of the sensing capabilities, and now with the new Whirlpool I either use Normal or Sensor with no options. All with brilliant results. Last night I used Heavy on the new machine and didn't honestly notice any difference in performance other than a longer cycle.
My philosophy is that if a machine can't perform with a full load of normally dirty dishes, meaning all scraped but never rinsed but nothing burned or scorched on, and not produce perfect results with its normal or regular cycle, it's not a machine that belongs in my house.
Now of course, if I decided to put a casserole dish or something with burnt on food, that would definitely warrant no less than the P&P or Heavy cycle.