I think that the exit interview is
always worth doing if there are real problems with how the unit/facility functions. Even if it seems that higher administration just isn't interested, there's value in adding your opinions to "the pile;" if they get
enough reports of the same problems,
eventually they may be motivated to make changes. If everyone who leaves because they're unhappy working there assumes that her/his opinion doesn't matter and isn't going to make a difference, then nothing's going to change. And, obviously, if you're leaving because you just can't stand your boss anymore on a personal level, there's no point to reporting that to the administration. But if your boss is running the unit in a way that creates problems for the unit and staff, that is something that can be reported and discussed in an objective way, without getting personal or emotional (and, IMHO, you should use the exit interview to report any other types of general, "systemic" issues/problems that impacted your decision to leave). Go in to the interview with constructive suggestions/examples of how the situation could be improved, not just complaints.
I had this exact experience many years ago; I left a job because the NM of the unit was a very troubled woman who took out a lot of her dysfunction on her staff. When I left, I had an exit interview with the DON and was very open about why I was leaving (not that I "didn't like" the NM or "she was mean to me" (although both those things were true!

), but specific examples, including dates and other people involved, of actions/behavior of hers that impacted negatively on the staff and the quality of the program provided to the clients). I knew as I was saying it that they had heard all the same stuff many times before, and they thanked me warmly and sent me on my way and I figured that was the end of it, but I heard later from someone who still worked there that, shortly after I left,
another person complained and this time she was fired. Sometimes it's just a matter of reaching "critical mass" with the negative feedback about a particular issue (and, when it's a matter of firing someone, the facility, for its own legal protection,
has to establish a clear "track record" of problems over time and the individual's failure to improve despite being counseled -- so that requires multiple complaints from others over time).
I certainly agree that it's important to be thoughtful and professional about what you choose to share in an exit interview, so as not to leave on bad terms.
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