Hello, 

What PRPC version is it? HELP file should be saying something like: 

Three activity lists are maintained for each requestor, stored in Java constructs. The lists are:

• Current list — highest priority
• Activity list — intermediate priority
• Workflow list — lowest priority

Use this method to add an activity to one of the three lists, as an alternative to a Call. If the activity requires parameters, enter literal parameters in the method's parameter fields.

This method does not check the validity of the activity you add. Make sure that the activity exists and that users have the necessary security to execute it.

Pega 8.3.
I would like to know some real time scenarios.