[dxhdr]

> High fidelity operational metrics have a useful half life measured in days or weeks.

It depends on how high fidelity you're talking but in my experience retaining these metrics can be valuable, not only for viewing seasonal trends already mentioned in another reply but for debugging problems. It can be helpful to be able to view prior events and compare metrics at those times to a current scenario, for example as a part of a postmortem analysis. I do agree that the usefulness of old metrics falls off with time. Metrics issued from a system 3 years ago likely have little in common with the system running today.