Which term describes something that is advantageous or useful?

The term that describes something advantageous or useful is "expedient." This word is often used in contexts where a particular course of action is not only timely but also beneficial in achieving a desired outcome. In various situations, something that is expedient may effectively serve a purpose, often in a practical or pragmatic manner.

In contrast, "gratuitous" typically refers to something that is given or done without charge or justification, often indicating a lack of necessity. "Spurious" denotes something that is false or not genuine, which starkly contrasts with the idea of being advantageous. Lastly, "unremitting" describes something that is relentless or constant, but it does not carry the connotation of being useful or beneficial. Thus, "expedient" stands out as the most appropriate choice to convey the idea of something that is advantageous or beneficial.