DEV-00762 USB Bitwacker: What was the PRG button used for?

Does anybody know whether that PRG pushbutton is really needed? / what it is used for?

I plan on programming the PIC myself, but I don’t know any reason I would need that button.

It is used to put the board into Programming mode; https://www.sparkfun.com/datasheets/Dev … 0Guide.pdf has a guide to its use