Brine shrimp (Artemia salina) is a small filter-feeding crustacean that lives in saltwater habitats. They grow to about 0.4 to 0.6 inches and take about a week to mature depending on the conditions. After they mature, they can live for several months and produce as much as 75 eggs every day. They live in a wide range of different habitats inland and on the coast. These creatures have exceptional resistance to changes in temperature and salinity levels.
Their gills allow them to be in these conditions by absorbing or extracting ions as needed. This allows them to live offshore, in lakes, and man-made bodies of water in most parts of the world. To eat, they use their legs to filter feed algae off rocks. They also rely on phytoplankton in the water. As saltwater aquarists, our main goal is to replicate the natural environment of the ocean as accurately as possible in our reef tanks. In natural reefs, fish do not get fed flake food or frozen food.
They hunt and eat live organisms enriched by nutrients from natural environments. Why would we not at least attempt to do the same in our aquariums? By feeding live food, you are more accurately replicating the ocean environment from which they naturally live in. A more popular reason for feeding live brine is to meet the needs of finicky fish.
Fish such as dragonets, butterflies, or anthias are all fish that are known to be difficult to keep successfully because of their dietary needs. Live food can be used to train the fish to get used to eating a certain kind of food that can also be fed frozen. You could also regularly feed live food, which would be best for the fish but not required.
You may find an increase in the vibrancy of the colors on your fish. Fish that are fed healthy foods such as live brine shrimp, will be less susceptible to disease and will live longer overall. You are not expected to feed live foods every day, but it is worthwhile to feed live food once a month or even twice a month.