There are two parts on this approach. The 1st one is the positive "hey, chillax, transfer knowledge, don't be stressed, etc." The 2nd is security: "this guy cannot be trusted to 'touch' anything, we don't want him to plant a timebomb, we don't want him to mess things up, etc."

It's not 'polite' to bring up the 2nd, but it _is_ there. Imagine me/you/him/her doing something wrong and bringing down Prod for X hours. Then imagine your manager telling the director "oh, and btw he submitted his resignation 2 weeks ago, and in confidence he told me he goes to our ABC competitor". That-Looks-BAD, even if it was the most honest of mistakes and even someone else's fault. Once you 'stop playing', don't touch that jenga tower!!