For me they serve many purposes, first, I think having them makes the Passport look more rugged and SUV-like and less Mini-Van-like. Next, I am hoping they do help stop rocks and things from hitting the sides of the car. Next. I hope they serve as a reminder when some brain-dead parks next to me, to be careful when they open their car doors ( I do not want Body Side Moldings). Lastly, I do use them, even at 5'9" I like stepping up into the Passport.
Also: I do have the Die-cast Running Boards, again because the look better than the plastic ones (IMO) and have suffered a "rug-burn" on the back of my leg, when wearing shorts and sliding out of the vehicle - without stepping on the Running Board (ouch!)..