A varied diet — a quality staple food plus occasional frozen or live foods and, for some fish, vegetable matter — keeps fish healthier and more colourful than a single dry food alone.
Match the food to the fish: floating flakes suit top-feeders, sinking pellets or wafers feed bottom-dwellers like corydoras and plecos, and herbivores need algae or veg. One food rarely suits every fish in a community.
Quality and variety matter more than quantity — see overfeeding for why less is usually more.