I no longer have a high efficiency washing machine. Now that I have a set of Speed Queens, they require much, much for water than my old LG HE set. The laundry pro slows down the cold water going into the washer so it can oxygenate it. If your washer uses only a few gallons it's immaterial. But, if your washer fills with 22 gallons, it increases the total time by at least 15 minutes due to the reduced water flow into the machine.