The phrase "be of useful" suggests something that serves a purpose or fulfills a need. Synonyms for this phrase might include "be beneficial," "be helpful," "be valuable," or "be practical." Other possibilities include "be productive," "be profitable," "be advantageous," or "be constructive." Each of these words carries its own nuances and connotations, depending on the context in which it is used. Regardless, they all imply that something has a purpose or utility, and that it can contribute positively to a situation or outcome. Whether in a personal or professional setting, being of useful is a desirable trait that can help individuals or organizations achieve their goals.