There are many synonyms for the phrase "are useful." Some examples include "are advantageous," "are beneficial," and "are helpful." Additionally, "are valuable," "are practical," and "are functional" can also be used interchangeably with "are useful." Other synonyms that may be fitting in certain contexts include "are favorable," "are convenient," and "are productive." Whether you're looking for a more specific way to convey the usefulness of something or simply want to add variety to your writing, these synonyms can help you effectively describe the benefits of a particular item, concept, or idea.