It really depends on if you have a dishwasher that relies on evap for drying, or an explicit heating element. The latter is becoming more rare as time goes on.
This is why rinse aid is critical, you have to minimize the amount of water on the dishes. The extremely hot water tends to heat up the dishes enough so they retain enough heat to evaporate off the rest of the water. Plastic stuff like cups tends to stay pretty wet since they don't have the thermal capacity of metal or porcelain. A big advantage with this design, other than the energy savings, is that you don't have to worry about putting plastic stuff on the bottom rack, since there's no localized source of heat that can melt them.
I don't bother; I've tried it and haven't observed any effects.