The 'PU Comp' adjust the amount of compensation (extra volume) in the single coil positions (2 and 4 with the HH, 1-4 with the HSS). Raises the output so you can match the humbucker. (Personally I turn that off ... I want those positions to be quieter.)
The bottom two are for the Silent Circuit adjustments. Since yours is an HH config you don't have a Silent Circuit.