No, you don't have to thaw frozen potatoes before cooking them. In fact, it's not even necessary to defrost them; you can cook them straight from the freezer. However, if you're planning to fry or bake the potatoes, you'll get better results if you let them thaw first. When frying, this will help the potatoes cook evenly and prevent them from sticking to the pan. And when baking, pre-heating the potatoes will help them cook faster and more evenly. Of course, there are always exceptions to the rule. If you're in a hurry and need to cook the potatoes right away, then go ahead and do so without thawing them first. But in general, it's best to thaw them before cooking.