When processing a wage type, there is no requirement to differentiate between employee subgroup groupings.

When processing a wage type in SAP Payroll, if there is no requirement to differentiate between employee subgroup groupings, you would leave parameter 3 blank when function PIT calls the rule to process the wage type1. This is because parameter 3 in the PIT function is typically used for relative time unit, and if set to ‘X’, it would mean WPBP for each time unit1. However, in this case, since there is no differentiation needed for employee subgroup groupings, parameter 3 should be left blank. References = 

https://community.sap.com/t5/enterprise-resource-planning-blogs-by-members/understanding-functions-in-payroll-schemas-specific-eg-wpbp/ba-p/13270777