The Compensation of the Employee will be effective in payroll from the selected 'Effective Pay Period Date' in the Compensation.
For Example:
The Effective Pay period date of an employee is 01-Jan-2018. Now if we run the payroll for the previous pay periods (Jan-2017 to Dec-2017) then that employee will not include in those pay periods.
That employee will include from the Pay period Jan-2018 in Payroll.
Hope your query is answered !!!