In the summer, mulch helps the soil hold moisture so you don't have to water your garden as often. In the hot sun.
Mulch also prevents weeds. Adding mulch to your planting bed will block light from openings in the soil, therefore inhibiting weed germination. It also provides soil insulation, which helps control soil temperature and saves plant roots from extreme heat as well as freeze.
Over time, mulches made from organic materials break down and increase your soil's structure and fertility aiding in plant growth.