Generally most KPI are a waste of time and effort. Most are ‘so what’ KPI. They are isolated KPI that do not contribute to real business benefits. Some are mainly output related rather than throughput related; Example case is inventory versus throughput.
The key difference is that throughput is based on what is actually billed and delivered, while output is something produced and sitting in inventory providing zero value to the organization. Fundamentally throughput relates to cash flow, productivity and profitability; the key elements of any success factor of an organization.
Having throughput as a KPI measure provides the ability for any organization to achieve its goal; the goal of being profitable and ability to grow. The rest has no relevance.