Answer:
The very purpose of JIT is to reduce inventory at all places in the supply chain. Inventory is considered a waste because inventory is created by using materials, machines, and efforts of persons. All of these are resources which have already been used up and that portion of it which is not consumed and sent up the value chain causes a drag in the system.

However, inventories are inevitable because uncertainties exist at every stage, making it necessary to provide a buffer so that demands do not go unfilled. The challenge is to keep it to the minimum. To make this happen, the calculations involving the following are necessary:
o   Forecasts of the market demand
o   Capacities of the equipments
o   Worker absenteeism
o   Supplier’s lead times
o   Quality of the produced components