I use sound from behind all the time. There are several spots on my training routes that have bad pavement and holes on extreme right side near shoulder. If possible I need to avoid them and ride closer to middle. But they are also in extreme downhill sections where I am at speed and in corners where it's not safe to look behind. I give a quick look behind before I start the scetions, then I use my hearing most often to ascertain if anyone's close behind and if I need to move to right. I do this things without an real thought - I've been riding so long that using hearing with vision is just part of how I ride.

But that's just me. I can't dictate to anyone about using music. I just think it poses more risk, and more risk than I am willing to assume.