When measuring employee performance, it may in some jobs be possible to track the ways in which the employees physically move about the workplace. In other jobs, it may be possible to use traffic in such things as emails as a way of evaluating employees. This will be most applicable to jobs that do not have a tangible output that is easy to measure.
In a job where output is hard to measure, we might be able to use physical or email traffic patterns to evaluate how well individual workers are doing. For example, if we have the proper technology, we can track where workers go during the course of a day. The more that they are interacting with coworkers who are in relevant positions, the better. Each of these interactions can lead to ideas about how to do the jobs that they are working on. In this sense, a worker who is communicating often with other workers, whether in person or by email/messaging, is a worker who is more likely to be doing a good job.