The term "be of advantage" refers to a situation where someone benefits from a certain circumstance or action. The opposite of this term is "be of disadvantage", which refers to a situation where someone experiences a loss or disadvantage. Other antonyms for "be of advantage" include "be of detriment", "be a hindrance", and "be a drawback". These terms describe situations where someone faces obstacles or difficulties that prevent them from achieving their goals. It is important to consider both the advantages and disadvantages of any given situation, as this can help people make better decisions and achieve their objectives more effectively.