Functionality provided by `etcd-server-events`?

I am investigating a k8s cluster with a single master where the etcd-server-events pod is failing due to a volume mount issue.

/var/etcd/data-events is now mounted read-only.
/var/etcd/main is still accessible read/write

The high-level purpose of etcd is understood, but is there a clear list of k8s functionality which is not supported or recommended without etcd-server-events?

Cluster information:

Kubernetes version: 1.8
Cloud being used: AWS
Installation method: kops
Host OS: centos
CNI and version: weave
CRI and version: docker