Sharing a job can be a good way to make sure nothing "falls through the cracks" when you are out sick or on vacation. Any user you share a job with has the same privileges you do, when working with that job. The other user can post or take down a job, extend or refresh a job, and even permanently delete a non-posted job. They can also copy, edit, and forward the job to others. You will not receive any special notification if someone shares a job with you, so it is a good idea to check the Shared Jobs listing from time to time.