Some payroll items can be included as part of the employee's paycheck and some payroll items can be paid to the employee as an Unscheduled Payroll check. For example, consider a bonus payment:
If you're paying a bonus at each pay period as an earning item, include the bonus item in the regular paycheck. Set up a bonus payroll item in the employee's paycheck or set up a bonus wage item in the Employee record.
If you give bonuses occasionally at your discretion for special occasions (for example, at the end of the year), create a bonus check for this special circumstance using Unscheduled Payroll (otherwise the bonus payroll item will keep appearing in the employee's regular paychecks).