Answer:
The sociological significance of categorizing groups into dominant and minority groups is that, by recognizing the predominance of a certain racial group over the other groups, it is also recognized that the influence of this majority group will be much greater, and therefore more defining in the decision-making process at a general level, than that which minority groups may have.
Thus, for example, recognizing the predominance of the white racial group in the United States over the Asian, Latin and black minorities, it is also recognized that whites have a greater political weight in this country and a greater decision-making power at the national level than that of the other racial groups.