A useful KPI answers three questions: what changed, why does it matter, and what can the team do next? If it only reports activity, it may be a useful measure but not a key performance indicator.
Define the population, time window, calculation, and owner. Those details should be easy to find beside the number rather than hidden in a separate document.
Review KPIs regularly. When a measure stops changing decisions, replace it with a better signal instead of collecting it forever.