Foiling turns bar-b-q'ing into a different technique. Essentially, when you wrap the ribs in foil, you are now braising the ribs -- just like you would braise a pot roast. Braising produces a very soft, moist, fall of the bone texture.
Personally, the only time I foil ribs is when I have a left over slab in the fridge and I want to heat them up in the oven the next day. Foiling might also be a good way to keep ribs hot or "on hold" in a 150 degree oven.
I don't really agree with the idea of using foil to keep the ribs from getting too "smokey". If you need the foil for that, a better solution is probably to use less raw wood and less smoke.
But, there are lots of ways of skinning a cat.