You've already pointed out that this is basically unheard of but I'm struggling to think of situations where scrum metrics have provided benefits that outweighed the cost of taking, and exposing them.

My experience has been that most development teams intuitively recognise problems that might be revealed by these metrics. Is this not often the case?

The thing is with metrics is that they are hard to argue with, whereas intuition is a debatable opinion. Perhaps not everyone in the team agrees. Perhaps it's about showing interfering management or dependent teams where the issues lie. Perhaps the team doesn't realise how long a particular stage in their workflow is holding things up - I mean they know that stage is a problem but have they realised it's actually their biggest blocker to finishing work?

Also depending on what you use to generate metrics - something like ActionableAgile that use Monte Carlo simulations against a few weeks worth of activities can show a team what their cycle time is, what items are in danger of blowing that and how long it's likely to finish just their current backlog (for example).

As you say, in their worst case they tell teams what they already know and then again that's the value of a good SM or AC - finding out why nothing is being done about it (whilst beating away interfering managers).