Same person as supervisor/co-promotor and professor/promotor I've just started a PhD. Currently I only have one person who is supervising me (the professor). So he is now both my supervisor and my promotor.

Now other (ex) PhD students are telling me that these roles should be filled by different people, to prevent mix of interests. But I don't have sufficient insight on what they are referring to.

Should I be worried? Should I talk to my department head to change the situation?

edit, let me clarify:


With "promotor" I mean the main project supervisor, being a professor. He has the final responsibility.
With "supervisor" I mean the daily supervisor, sometimes also called co-promotor. To my understanding this is often somebody else, for instance an associate professor or assistant professor.
Considering German institution/university where I am doing my Ph.D. now, you are the person who is responsible for finding a second supervisor to your thesis. 


Regulations for Doctoral Degree Studies in Germany says (computer science field):


§ 3 and § 4 § 3 II (Primary Supervisors):
“Professors and lecturers who have completed their post-doctoral qualifications, are members of the faculty, or were included in the acceptance of the dissertation, can be primary supervisors.”

§ 4 II (Secondary Supervisors):
“Secondary supervisors assume a supervisory and consultative function. Professors and university lecturers with post-doctoral qualifications can serve as secondary supervisors. The Doctoral Committee can authorize additional scholars and scientists to serve as secondary dissertation supervisors upon case-by-case assessment and the issuance of a resolution to that effect. They need not belong to the faculty.”