The advantage of a multi trip / annual travel insurance policy is that there is no need to worry about arranging cover for each journey you take and it's usually better value than buying individual policies for two or three trips a year.
Most multi trip / annual travel insurance policies allow you to travel as many times as you like in the year as long as each trip is not longer than 45 days. Ski and snowboarding insurance is sometimes even covered for free with an annual travel insurance policy. Most activity and outdoors sports can be covered, from skydiving to walking.
Multi trip/annual travel insurance is an even better deal for families. Insurance for a couple will be cheaper than for two single adults and cover for a family with children under 18 is not usually much more expensive than cover for a couple. Do watch out for restrictions on how the cover works, though.