At the moment in my job site expired jobs redirect 301 to a deleted-page.
This prunes expired content and also causes less web clutter.
But I've seen many job sites keeping even old jobs which are in fact no use to visitor.
It is well known that it takes 2-3 years to rank well for a web page in Google. A job ad expiring in a month will have no page rank importance for Google and it does not know in advance that that page is going to be deleted very soon.
So which way should I go? Keeping expired content or deleting it promptly when it deems not useful anymore.