Our cloud bill went up again last month. Not because traffic exploded — traffic was fine. The cluster just… got fatter. More nodes. Same apps. Same user count. When I dug into it, the villain was not a runaway Deployment. It was a dozen YAML files where someone typed cpu: "2" and memory: 4Gi because that felt safe six months ago and nobody ever looked again.
Kubernetes will happily reserve capacity you never use. The scheduler only cares about requests. Your finance team only cares about the invoice. Those two facts meet in the middle as slack — resources booked, paid for, and idle.