In this k6 documentation https://grafana.com/docs/k6/latest/using-k6/scenarios/concepts/arrival-rate-vu-allocation/, there is a formula for preallocated VUs or virtual users

preAllocatedVUs = [median_iteration_duration * rate] + constant_for_variance

I don’t understand how they came up with this formula. Can someone please explain it to me with an actual example(s) ? If I need 30 iterations per second for 30 seconds, then do I always need 30 or more preAllocatedVUs or can I use less ?