Effectiveness is more important than Efficiency
Lisa Lang says:
One of the ways we typically apply efficiency in a job shop is by keeping all our equipment and/or people busy so that we don’t waste any capacity and have the highest possible utilization.
But this is baaaaad.
For business application, see her post on Continuous Improvement.
For a more personal insight into the difference between being effective vs being efficient, check out the Success Matrix Productivity Principle 6: Be Efficient.