The practical effect of Charlemagne accepting the Pope's offer to be crowned Holy Roman Emperor in 800 was primarily:
A. proving that the Pope was as powerful as the Byzantine emperor.
This act symbolized a significant shift in power dynamics, showcasing the Pope's authority in crowning a ruler and relating closely to the Byzantine Emperor, who had previously held that title. It was a statement of the Pope's influence in political matters and the relationship between church and state.