Body Glide (and similar products) "stops friction and creates a protective barrier on your skin -- preventing chafing, blisters, rash, saddle sores, and skin irritation" use it "anywhere skin or clothing rubs against skin during activity".
I use it on my feet with sandals that rub, and where my shorts/thighs rub and on my shoulders when wearing a backpack...also my ds likes it on his groin area guess it keeps things from rubbing against ohter things