I think the most underrated of the benefits of agile software development is the feature- and delivery- focused feedback loop.

The ability to get project feedback in weeks instead of months, using comprehensible, real-world metrics is something that any operational manager should instinctively appreciate.  In fact, I suspect that if you were to rename agile development to “feedback-focused development”, we would all find it easier to sell agile software development  tools, techniques and services to your average development manager

Why do I think this?   Because a good operational manager understands that feedback and ongoing monitoring is critical to the success of projects and companies.  Imagine a surgeon who didn’t bother hooking his patient up to a heart rate and blood pressure monitor - who put her under, started cutting, and only stopped when he noticed that the patient’s skin was turning white and translucent because bloodflow had stopped.  Does that sound like a good way to go about performing surgery?
No, of course not.  And in software development, the metrics that are meaningfully equivalent to a steady heartrate and a stable blood pressure are the delivery of tested features.  Not the documents, describing what the features will do, Not the the delivery of the test plan, representing what the QA team will test once the software is out of devleopment, and certainly not the 80% complete bar on the Gannt chart representing how much of this particular technical element of the feature is done.
“But the documents are important.  you wouldn’t want the surgeon to cut without a plan.”  Of course a plan is important.  Agile development does not neglect planning; on the contrary, it centers the planning around the need for a feedback loop.  Because as every operational manager knows, planning is part of the project.  if you can’t get meaingful feedback, the planning phase of the project is a black hole, a big question mark in the middle of the project that the manager has no ability to measure or influence.  And no operational manager should have to work under those conditions.  And neither should anyone else.