Mutually useful is a phrase that is often used to describe a relationship or partnership that benefits both parties involved. It is a common term in business and personal relationships alike and is often used to describe situations where both parties have something to gain. There are many different synonyms for this phrase, including mutually beneficial, mutually advantageous, and symbiotic. These words all describe a situation where both parties benefit from the relationship, and they can be used interchangeably with the phrase mutually useful. Other synonyms for this phrase might include cooperative, collaborative, and supportive, as each of these words also describe a situation where two parties work together to achieve a common goal.