Controlling The Worker Bees

Part of the busywork problem is some managers equate busyness with productivity. 

The perception is not just that a busy worker is engaged and making an effort, but even that their industriousness gives them a higher moral value than their less busy colleagues. This sets up a dynamic in which two office workers completing identical tasks can be judged on their busyness, rather than their results.

Who appears to be more engaged: the busy worker who skips lunch to get things finished, or the efficient worker who finishes early and uses the time saved to buy groceries online?