Adding ITP/Document Processors can improve performance when requests often have to wait for each other to be processed. In that case adding the capability to process requests simultaneous will greatly improve performance. A simple test to recognize this situation is to use the System Monitor. If ITP/Server appears slow but the processor is not that busy, chances are processes spend most of their time waiting.
Refer to the Help of the Administrator for details on how to add an ITP/Document Processor.