Not really an advantage of triples. It's the cherry I put on top of them, and it works arguably just as well, if not better, on a single screen.
No audio spotter is as good as visual information. Verbal spotters are fun and plenty swear by them, but voice has a delay and you still need to process what you hear. Speed of sound is fast, but we need a spotter at the speed of light.
Triples plus a wide virtual mirror gets you most of the way there. There's still a small blind spot between the main screen and the mirror. The fix is a blind-spot indicator overlay. I use the ones in RaceLab. Within a week I'd stopped turning Crew Chief on. I just didn't need it anymore.
How they work
Small coloured dots on the outer edges of your main monitor. When the dot is on, there's a car there. When it's off, you're clear. That simple. In three-wide situations they completely crush an audio spotter, because your eyes never have to leave the apex.
Back when I was on a single 43 inch TV, these indicators let me race unbelievably close to people and know exactly when I could close the door without risking contact. Turn them on. Learn to trust them. In my experience they don't lie.