If an employee's pay is calculated using their Recurring Pay plus timesheet entries and activity hours are on their timesheets

Keep in mind that salaried employees are always paid their recurring pay, as are hourly employees for whom you've selected to use Recurring Pay values in addition to Timesheet entries to calculate their pay.

If you choose to include activity hours on a timesheet, these employees are paid for the activity hours in addition to their recurring pay amounts. If you want to track the activity for invoicing but don't want to add the hours to their pay, simply don't mark the checkbox.