well it seems to me that if I have the nut flush draw and say bottom pair and nothing else, I might jam against a (probable) top set, given the dead money and some fold equity if the guy doesn't have top set
if two of my buddies at the table showed me their cards and they had none of my suit in their 8 cards, and they had 4 pair cards (matching the board) in their hands.
http://twodimes.net/h/?z=2753027 30% equity
http://twodimes.net/h/?z=2753059 40% equity
maybe not the best example but you see the point.