Multiprocessing: long and short workers

I am trying to do something multi-processor with a distributed queue. Is there a reason to choose run

over run2

? My feeling is a run2

little more effective as it doesn't have the overhead of returning control to the main process.

from multiprocessing import Pool
from foo import my_distributed_queue as queue

def process_msg(msg):
  foo(msg)

def run():
  pool = Pool(4)
  for msg in queue:
    pool.apply_async(process_msg, (msg, ))

def process_msg2():
    for msg in queue:
      foo(msg)

def run2():
  pool = Pool(4)
  for i in range(4):
      pool.apply_async(process_msg2, ())

if __name__ == '__main__'
  run()
  #run2()