How would antipsychotics help depression?

Sometimes needed: Occasionally, use of regular antidepressants alone cannot control moderate to severe depressive symptoms. In these cases, certain atypical antipsychotic e.g. Abilify (aripiprazole) and Risperdal can be helpful. These medications should be prescribed by a physician with experience.

Major depression: If major depression is severe enough there can be psychotic episodes experienced by the patient, so yes, antipsychotics could be used in a worst-case scenario.