Among many hundreds of visas over the years, perhaps a dozen went unused. I've never had that be any issue whatsoever... either in applying for subsequent visa (such as in China or various Mideast countries), or in PP renewals, or in arrivals overseas or back in the US. Other than a myriad of reasons as to why a visa would go unused, nothing singularly nefarious comes to mind that would cue an immigrations officer in the absence of any other suspicious elements.