I took up skiing and skating to get over some fears of mine (heights, speed, falling etc) and so that I could enjoy those sports in places I hope to visit some day (Chamonix-Mont Blanc, Kitzbuhel).
Another large reason, it to help keep my metabolism and overall energy level higher during the winter months.
You see, I naturally want to hibernate and eat when the cold weather comes.
Our society makes most of us work throughout the year, regardless of whether our bodies want to do not. It causes a lot of stress to go against our natural grain like that. Perhaps that is why a lot of us want to retire early -- in order to finally live according to natural cycles? I know that is true for me!
Winter is the season where the decreased sunlight triggers a hibernation response in humans and animals. Those of us with a winter would know what I'm talking about. We are not that much different than the bears!
I know of people who are prone to depression during the low sunlight times of the year. I know of people who use tanning salons to get their UV fix and claim to feel much better (same with people who head South for the winter). I know of people who use special full spectrum lamps at home for the same reason.
We heal and regenerate during the "down times", our nightly sleep, seasonal hibernation and siestas etc. I personally feel we don't have enough down time at the right times.