There's at least one case in which pushing for maximum efficiency can actually slow down an operation. This particular instance involves a certain muda I didn't discuss in my "Lean on the Green" series: defects. If something goes wrong in your process, and you don't catch it promptly, it's going to cost you. When it comes to quality control, it's pay now or pay later. Every step in the process adds to the potential cost of a defect, and the farther along the flow unit gets before a defect is found, the more it costs to start over. This cost is especially bad if you don't catch the problem until after your flow units have passed through the bottleneck. Before that point, each of your resources has some capacity to spare, so that the extra motion won't be too taxing. But the bottleneck by definition is already operating at capacity.
Keep in mind that a flow unit can be anything that undergoes a defined process, whether it's a widget on the shelf or a customer in the store. Just as you would want to inspect materials or ingredients early in a process, you want to verify the quality of your customer's experience before they get too far in.
All of this is one more reason to identify your bottleneck, so you know where to concentrate your quality control, and also to anticipate normal attrition, lest you count your chickens before they hatch. Stay tuned for a complete demonstration of how to make these calculations.