If it hasn't rained for awhile, you'll notice that the top of the leaf layer is dry. But, turn it over and you'll see moisture on the leaf litter and on the soil. Put your hand on the moist ground that was covered by the leaves and you'll feel that it is cool to the touch. You might also see all kinds of little critters, like earth worms and other bugs that are eating the mulch, breaking it down and making the nutrients available to the plants that are growing nearby. This is how topsoil is made.
Soil life is possible only when there is food, water and shelter.
Nature provides the food and shelter each time a leaf falls onto the ground. When soil is uncovered it becomes vulnerable to the ravages of the sun, wind and rain. Baresoil also can't provide food and shelter to all the critters that help break down organic matter and keep the soil alive. As gardeners, we want healthy soil that is teeming with life so our plants that we spend time and money on and build our passions around can thrive. Applying mulch to our gardens mimicks how nature cares for plants in the wild.