In manufacturing, inventory is a waste because it’s not being sold. It’s in a warehouse collecting dust not payment. Therefore, it’s waste. Lean manufacturing strives to keep inventory to a bare minimum and use a JIT (just in time) methodology that only produce what is needed when it is needed.
In a service business like staffing, processing more people than can be put to work is waste—especially when we have “inventory” we never use, never place and especially given the shelf life of talent is about 2 days in the current economy.
No one can ever get to zero inventory but that’s the goal. Inventory literally costs companies millions!