At first I thought this was about setting up Kubernetes clusters, but that is not what this is about at all. The cluster is just providing resources, the actual thing here is multiple environments within that cluster. So you might have your chain of services (frontends, backends, event based services) and instead of duplicating all of them you somewhat nest them blue-green style in the same cluster.

In theory you could just use ingress and a special URL to deploy a single service as a special one-off deviation, but when you want to have an entire chain of services adjusted for a separate virtual environment that no longer works (unless you duplicate all services and rewrite all dependant service URLs for example).