Frozen food is a great way of getting nutrients into your fish without the hassle of having to keep it fresh or buy it from the store on a regular basis.  It also allows for feeding a variety of foods with the addition of beneficial vitamins and fatty acids to keep your fish healthier and more vibrant looking.  To avoid excess nutrients getting into your aquarium you may want to rinse your food or let it thaw on a paper towel as frozen food can add phosphates into your aquarium and fuel algae growth.  Be sure to provide the proper type of food for herbivorous fish or carnivorous fish or invertebrates.