I had a very cold and windy hike in SNP over the weekend where I wished I'd had a hood. My partner had one and was pretty doggone happy about it. In the end, it was so cold and windy that we decided to bail on the plan to spend the night and start hitching back to the car. When it is that cold and windy, there is no combination of hat and gaiter/buff that work as well as a hood. Of course, some combination of those things is more than adequate the vast majority of the time.