Last night I ran five miles on the trails at the Mines of Spain. The reason being that I have been having all sorts of lower leg problems. In short, a muscle gets overworked, or underworked compared to it's opposing muscle, and it hurts. Running is very repetitive. Trail running breaks up the monotony. Every step is a twisting uneven adventure of an ankle roll waiting to happen.
The uneven nature is a huge advantage. Because every step is slightly different the muscle fibers used are slightly different on every step. So "little" muscles on the sides and front of your feet are strengthened. It is important to maintain a balance between the muscles in your body. Otherwise injuries will develop, especially with repetitive use activities like sitting at a desk or running.
The other positive advantage, especially during this time of year, is the scenery. The leaves are changing colors. There are no vehicles to dodge. It is quiet. It is surprising how even half an hour out in the woods away from the hustle and bustle of the "to do" list is so relaxing. We still have a week or two left of leaves changing colors! Go get some trail therapy! I know I will.