Rinse aid is a surfectant, meaning it lowers the surface tension of water, so it more easily slides off dishes in the dishwasher. Especially in hard water areas, rinse aid helps prevent water spots from forming on, for example, glasses, plates and cutlery. It also helps dishes dry faster. Now, if you have a soft water system do not use as much. If you don’t use the rinse aid then you could have spots on glass from hard water.
Helpful Hint: when emptying dishwasher pull out bottom rack first to empty. This will keep the plastic dishes in the top rack from making them wet again.