Question: "What is RAP?" or "What is the difference between RB Pro and Enterprise?"
ReportBuilder Enterprise includes a run-time Pascal environment called RAP. RAP enables developers and end-users to code without Delphi. RAP code can be used to add calculations and event-handlers to reports.
"Why use RAP? or "Why would I use that?"
RAP code is stored as part of the report definition. (Delphi code which is compiled into the .exe). In other words, report definitions loaded from a database or report file can contain the RAP code required to run the report.
You can optionally include RAP in end-user reporting solutions so that end-users have the power to add code to reports they create. (End-users do not have Delphi)
RAP code does not require that you compile your Delphi project to see the results. This speeds up the design/preview process. (Typically while creating reports you want to make changes and preview the results, then make changes, preview again, etc).
More information on RAP:
Website
http://www.digital-metaphors.com/products/RAP
Learning ReportBuilder RAP
http://www.digital-metaphors.com/download/learning_reportbuilder.html
Download a trial version of RB Enterprise and run the RBuilder\Demos\RAP examples