There are two benefits to partially cooking the potatoes in the microwave. The first benefit is it shortens the overall time to complete the recipe. The second benefit is to avoid overcooking the cream based soup (i.e. reduce the risk of scalding) and overcooking the other vegetables. Also, I want to mention this chowder is not the thick, heavy type. This chowder is a cream and broth based soup that has substantial body as in it coats the back of a spoon very nicely. If you like the thicker version clam chowder, you can add additional butter and flour after the vegetables have been cooked to create more roux as a thickener.