In certain IPI installations, vSphere and Baremetal, the external traffic reaching the IngressVIP is not balanced between the default ingresscontroller replicas.

In the "Understanding the Ingress Operator" page:  
- https://docs.openshift.com/container-platform/4.15/networking/ingress-operator.html

In sections:

- "Autoscaling an Ingress Controller"
- "Scaling an Ingress Controller"

Should be mentioned that if the installation is vSphere IPI or Baremetal IPI scaling the default ingresscontroller will not improve the performances if an external load balancer is not configured too.

The same should be mentioned in the "Optimizing routing" page:

- https://docs.openshift.com/container-platform/4.15/scalability_and_performance/optimization/routing-optimization.html

In section: 

- "Baseline Ingress Controller (router) performance"

All the supported versions