I know the purpose of other Kubernetes default namespaces such as: kube-system, default & kube-public, but there is no official document about the kube-node-lease.
The only official explanation I've found is:
Heartbeats, sent by Kubernetes nodes, help determine the availability of a node. There are two forms of heartbeats: updates of NodeStatus and the Lease object. Each Node has an associated Lease object in the kube-node-lease namespace.
With kubectl get all -n kube-node-lease I'm getting no resources at all. (k8s-version: 1.15)
here is the Kubernetes Enhancement Proposal of node-heartbeat.md for this feature. It makes node heartbeats significantly cheaper from both scalability and performance perspective.
This introduce a new Lease built-in API in the newly created API group coordination.k8s.io. which makes it easily reusable for other purposes 3rd party device monitoring plugins that's why it is namespaced.
This feature become stable in k8s 1.17