There will come a time when running your test plans on a single machine won't cut it any longer performance-wise, since resources on the single box are limited. For example, this can be the case when you want to spin-off a thousand users for a test plan. Depending on the power and resources of the machine you are testing on and the nature of your test plans, a single machine can probably spin-off with 300–600 threads before starting to error out or causing inaccurate test results. There are several reasons why this may happen. One is because there is a limit to the amount of threads you can spin-off on a single machine. Most operating systems guard against complete system failure by placing such limits on hosted applications. Also, your use case may require you to simulate requests from various IP addresses. Distributed testing allows you to replicate tests across many low-end machines, enabling you to start more threads and thereby simulating more load on...