[ewilliams]

I interpret "waiting" very broadly as the enemy of lean. If machine X waits for the next part Y to arrive, conceptually X is the customer of the part Y flow, and X is losing time that can never be recovered. That matters IF operation X is a bottleneck in the broader scheme of things. It does not matter in the situation where, if X never had to wait, it could produce more product than the marketing department could sell. If part Y waits for machine X, conceptually Y is the customer of X, and Y is losing time it cannot recover in its urgency to reach the end of the supply chain. Again, that does not matter in the situation, where Y never has to wait, it would reach the end of the supply chain faster than it could be sold or consumed.