When you extend a job, your job candidate pool remains intact and new candidates will continue to be added.

When you take down a job, the candidate pool remains intact and the existing candidates are now associated with the non-posted job.

When you repost a job, you can choose whether or not to combine the candidate pool from the previous posting with new candidates that you receive from the new posting.

When you delete a job, its candidates are no longer associated with that job. This should only be used when you want to permanently delete the job and will have no further use for it in the future.