Reorder points, lead times, and supplier management. Getting purchase orders out at the right moment when your lead times are long and your suppliers are inconsistent.
Every inventory risk is the same risk arriving at a different time: you committed cash to a forecast and the forecast was wrong. The six ways that bill lands, which one to accept on purpose, and how to size the rest.
Demand planning asks what will sell. Supply planning asks what that costs in cash, capacity and lead time. How to build the second one, step by step, and what it catches that a forecast alone never will.