Answer:
An important advantage is the division of the work of the cells present in these organisms, saving energy and giving efficiency to the organism.
Being multicellular gave them an advantage over predation, for example, algae being larger were more difficult to eat.
This multicellular condition also allows them to feed on larger prey.
On the other hand, being multicellular gives them greater mobility by having more complex nervous systems. The evolution of multicellular organisms allowed an expansion in the colonization of new niches.