When we reach for it
Before a launch, before a campaign, and before any claim about capacity is made to a customer. A load test against a target nobody agreed to is theatre; against a written commitment it is evidence, and the difference is who signed the number.
When we would argue against it
Running it against production without a plan. A load test is an incident you scheduled, and it needs the same care. Load testing a system with no instrumentation tells you it broke and nothing about where, so observability goes in first or the result is only a graph going down.
What it looks like in delivery
A target agreed in writing first, a representative environment, and the result recorded with the method beside it. The environment has to be shaped like production for the number to mean anything, and we report what we measured rather than what it reassures anyone to hear.