What is the role of the principal? Does a conflict exist between your perception of a principal's role and his/her role as your evaluator?

Principal has a pivotal role in running an educational institution. He manages all the Academic activities of the institution. Sometimes the administrative duties are also handed over to the Principal. 

Principal being the head of the institution has the authority to evaluate the performance of all the subordinates accurately. 

In my opinion a good Principal use this power to boost the overall performance of the institution and not for the sake of satisfying grudges against his staff.