What are the benefits of a job description and how it may contribute to the delivery of the service?

i'm studying Cert.III in community services (childcare assistant). this is a question from the study guide "participate in the work environment". i saw a similar question and hope that this is enough extra info.
What are the benefits of a job description and how it may contribute to the delivery of the service?
If you give your staff a job description, then #1 that gives your staff perfect direction of what is their responsibility and what is not. #2 because then if your staff comes to complain about one of their duties, you can pull out the employee handbook and let them know that they agreed to the job description when accepting the job offer.
Reply:I answered this before. You can find this answer by looking up KSA's in IO psych. Io psych is an entire field dedicated to your question. Simply type in IO or KSA and read why your description has impact beyond the hiring process. This will require a little work on your part but will be research (objective) based and not opinion (subjective) based. Many people have spent countless hours in IO delving into this very subject. Good Luck!!!
Reply:Very good benefits.