Whether you snowboard or ski, balaclavas are designed to cover your entire head, neck and most of your face. A hood will do exactly the same job if it comes with a draw cord and you pull the cord tight around your face. The hood, however, can also be worn ‘open’ with your face fully exposed to the elements if you prefer. As well as keeping you cooler when open, a hood helps you look cooler when walking round town for some apres ski!
Most balaclavas are thin so can be worn under your helmet or beanie but most hoods tend to be made from heavier fabrics and are designed to be worn over a helmet of beanie if you like.