Capacity forecasting happens on a quickly changing landscape, so back-of-the-envelope approximation is not just acceptable — it is appropriate. Engineering disciplines have always used it; web operations is no different. Elaborate precision is often wasted because new code ships and usage shifts before the model pays off. The real skill is **calibrating detail to the decision**: knowing when detail is needed and when it isn't. Unnecessary detail means wasted time; lacking the proper detail can be fatal to a budget or a forecast. Match the precision of the math to what the judgment actually requires — no more, no less. --- *Source: [[The Art of Capacity Planning]] (John Allspaw, O'Reilly 2008) — Ch 1 — Goals, Issues, and Processes in Capacity Planning*