Besides coolness... in no particular order.
Get a proper cheek weld on an AR without muffs banging into the stock.
Helps keep from giving away your position (even when shooting with supersonic ammo)
Easier to communicate during fire.
Critters will sometimes not scatter and wait patiently as others fall over.
Teaching young kids to shoot.
It is simply far more pleasant to shoot without hearing protection.
Makes wife happy.
How else can you tell if the can you hit is aluminum or tin, or hear a bullet hit the ground then tumble away in a buzz?
And if you're at a shooting range with others... it's just being polite.
I haven't got the can for my Rem 700SPS .308 yet, but I soon will. If the stuff ever does hit the fan... I'm going stealth.
Shuuuush... be vewy vewy quiet...