Youtube :- https://youtu.be/YEKKFyqPKnY
Based on Adhoc payment configuration, you can add or deduct certain fixed amount in employee's salary.
Example :-
1. Suppose an employee has taken advance from company and now you want to deduct certain fixed amount from his/her salary, then you can do adhoc payment configuration for this employee
2. Suppose you want to add Travelling allowance for certain period, then in here also you can do the same adhoc configuration