If you answered because there was an advantage to being able to have more successful breeding and successful births...you would be right!   The more females he can attract the greater possibility that the eggs will be laid.  And the greater the number of eggs successfully hatched makes it more efficient for the amount of energy this has cost him.  This idea of energy 'conservation' is important in the big picture of reproduction for garibaldi and many other fish.  Because the male does not need to put a lot of energy into making sperm....he produces huge quantities in comparison to his size....he then has more energy available for guarding the nest.  It's the opposite for the female garibaldi.   She has to put a lot of energy into making eggs.  If she also had to guard them, she would not only be spending more energy, but be too busy to eat the amount of food needed to produce as many, or as high of a quality eggs.  So, this behavior may, in the long run, enable parents to raise more 'babies' or offspring, than they would otherwise, with less energy wasted.