Apparently what I understand is that if you want to use the In-Circuit-Debug (ICD) function from MicroCode Studio Plus you need a PIC which has a built in USART and this hw USART is used by the ICD. So you application running into the PIC under debug cannot use the USART for something else within your own code.
May be I'm wrong but this is what I understood. If this is true, it could be a serious for some application requiring the use of the USART.

pf