This 25 percent of the per diem is for other minor expenses. The regulations do not indicate what kind of expenses these are. Nor do they condition the granting of this part of the per diem on the employee actually incurring any expenses. It is up to the employee to decide whether to spend these funds and on what.  

The amount due to the employee depends on the country to which he or she is sent on a business trip and the duration of the trip. 

These rules will not apply if the employer decides to independently, comprehensively regulate the issue of business travel and exclude the application of the Regulation of the Minister of Labour and Social Policy of 29 January 2013 on the amounts due to an employee of a national or local government budgetary unit in respect of business trips. In practice, this happens very rarely.
 

Find more in the PRO HR November 2023