IBM Rational Performance Tester (RPT), as you know is a Load testing engine and allows the flexibility of playing around with the user load for its execution. You might also be interested to know if you can ramp down the users gracefully when these user data is made to put them in an infinite loop and running the test for a fixed time.
When establishing the stages of execution in a schedule, you may want to pull down the active virtual users at different intervals but may not find an option to do that in Rational Performance Tester.
You want 1000 users to run for 10 minutes and then ramp down gracefully. In such case, you can as well add a second stage to the User Load in your schedule as shown below.
RPT initiated the second stage once the first stage reached its intended user load. RPT would then recognize that 999 users need to be "cleaned up" to begin stage 2 and it would clean them up over a 5 minute duration (according to what I have above). The last user would end "on his own"; RPT doesn't let you specify a '0' in the User field.
So in more generic way, The explanation is that "Change Rate" could mean "Ramp Up" rate or "Ramp Down" rate depending on the context. If the current stage has more users than the previous one, "change rate" means "Ramp Up" and if it has lesser users it will mean "Ramp Down",
For example, the first stage may have 100 users and the second stage have just 1 user. The "Ramp Down" happens in the second stage.