I wear helmets on bicycles and the habit carried over to skis. The peripheral vision is restricted by the goggle, not helmet, so I don't buy the idea that it restricts the awareness. (I guess wearing one that is not snug will be a problem...) The reason that I started wearing helmet on bicycle is that there is still possibility you get run over by careless rider or drivers, and this also applies on slopes. I have spent more than 20 million yen on my brain. I sure don't mind sparing less than one-thousandth of this amount to add more protection to my head.