What is the advantage to a sessile animal to produce free swimming larvae?

A sessile animal to produce free swimming larvae has primarily and radial symmetry. The advantage of this is that the primary and radial symmetry allows for the animals to reach out in all directions from one center such as during feeding. Since they don’t have a high degree of controllable movement even during food collecting periods, they can travel much greater distances than the bottom-dwelling adults, increasing their range. Secondarily, radial symmetric animals are able to receive stimuli from all directions which have efficient defense mechanisms due to their radial symmetric distribution.