SSIS的Force Execution Value如何使用？

从Goole上搜到的问题，和我想问的一样：

In the Control Flow you can force the Executionvalue of a Task. There is the properties ForceExecutionValue, that you must activate, and the property ForcedExecutionValue for the value which should be the ExecutionValue. In the property ForceExecutionValueType you define the Datatype of the Execution Value.

So far so good, but in which way can I use this forced Execution Value?

For Example: - an Execute SQL Task executes an UPDATE-Statement that updated 3 records - in the property ExecValueVariable is the variable "varValue" - after that Execute SQL Task, there is a Scripttask with a messagebox, that shows the value of the variable "varValue" If I run the package, everything works fine. 3 records were updated and the messagebox shows the value 3.

Now I change the property ForceExecutionValue to True, and the property ForcedExecutionValue to 1. If I run the package, I expect a messagebox with the value 1. But I shows still the value 3.