How does cell specialization benefit multicellular organisms?

It can make the organisms more complex and specialized.

If each cell has only one job, then it can devote all of its time and energy to doing that job. For example, in a unicellular organism, the cell is very complex, since it has to carry out a bunch of different tasks. In complex multicellular organisms, however, cells each have a very specific purpose, and thus individual cells can be simple and efficient.