What does the rinse aid do?
Rinse aid is injected into the final rinse of the cycle, a very small quantity is all that is required. The ingredients of the rinse aid breaks the tension of the water surface (the water tension is what allows a water boatman to walk across the surface, it does not actually break the surface tension), this means that the water will run off the dishes, pots and pans more easily and quickly.
Removing the water quickly reduces the chance of streaking as well as the rinse aid putting a squeaky shine to the dishes. It also aids the quick drying of the dishes.
Care should be taken to wipe up any spilt Rinse Aid when filling the dispenser, leaving spillages in the dishwasher can cause over foaming when next used, with a breakdown a distinct possibility, as well as poor wash results such as a greasy film on glass ware.