As far as I can tell, using the DEFINE just tells PBP to use a shorter method of executing the instruction:

QUOTE:
Early PIC18Xxxx devices do not include the LFSR assembler op-code. By
default, PBP will not use the LFSR op-code but will use a longer method
instead. If the PIC18Xxxx device does have the LFSR op-code, a Define may
be added to the BASIC program to tell PBP to use it:

Define USE_LFSR 1