Potatoes grow under the ground, in dirt, which makes them dirty. (This is science.) If you are going to eat the whole potato—skin and all—you should wash it beforehand. Baked potatoes, roasted potatoes, skin-on fries—all of these spuds need a good scrubbing as a first step, before any further prep work or cooking is…
source https://skillet.lifehacker.com/rinse-potatoes-after-peeling-not-before-1845747686