Big piles of leaves aren’t just fun to jump in. They can be incredibly helpful in garden beds. During the fall and winter, rain, snow and freezing temperatures can cause exposed soil to erode. Nutrients like calcium and nitrogen get washed away, and the result is that, by the spring, our soil can be depleted and acidic.
http://www.vancouverobserver.com/life/why-leaving-your-leaves-loving-your-leaves