There are several major advantages to taking on Kubernetes cluster federation. As mentioned previously, federation allows you increase the availability and tenancy capabilities of your Kubernetes clusters. By scaling across availability zones or regions of a single cloud service provider (CSP), or by scaling across multiple CSPs, federation takes the concept of high availability to the next level. Some term this global scheduling, which will could enable you to direct traffic in order to maximize an inexpensive CSP resource that becomes available in the spot market. You could also use global scheduling to relocate workloads cluster to end use populations, improving the performance of your applications.
There is also the opportunity to treat entire clusters as if they were Kubernetes objects, and deal with failure on a per-cluster basis instead of per machine...