Payroll services means running your monthly salary cycle end to end: collecting attendance and variable inputs, computing gross to net against your salary structure, producing the salary register and payslips, and completing the statutory work that follows, provident fund, ESIC, professional tax and TDS. Use it when the people are already hired and the administration around paying them has outgrown a spreadsheet.
Payroll is not a difficult calculation. It is an unforgiving one. A missed PF challan date, a professional tax slab applied to the wrong state, a TDS projection that ignores a mid-year joiner's previous employer income, or a full and final settlement that drifts for a quarter each cost far more than the processing itself, in interest, in penalty, and in the goodwill of the person who was paid wrong.
So the work is mostly in the calendar and the inputs. We fix the cut-off date, the input format and who signs off, then run the same sequence every month against it. Payroll that varies month to month is not flexibility, it is where errors get in.