The main reasons to cut the potatoes and pre-soak in water are: To allow the excess starches and sugars to be removed from the outer surface of the fry strips AND to keep the potatoes from browning prematurely from exposure to air. Covering in water helps the potato from turning a dark color. Adding salt to the water to form a brine mixture may seem helpful and can impart a flavor to the potato strips, however, salt is a major contributor to the fry oil breaking down prematurely, so I don’t recommend it. There is a restaurant out in San Francisco that soaks their potatoes in a water and vinegar solution, it adds flavor to the finished fries but this water/vinegar solution in enough to brine the potatoes isn’t salt free. While 1 teaspoon of vinegar may not have sodium show up in the Nutrition Facts chart, 2 tablespoons will have 1 mg of sodium. The two step method is designed to rid the potato strips of excess water, so they turn out extra crispy the second time they are fried in oil. A typical Idaho russet potato is about 20% solids or starch and 80% water. Cutting the potatoes, blanching in oil and then letting the potatoes rest and frying a second time makes for an extra crispy fry.