Since they will be denied light, weed seedlings will not grow. Mulches insulate plants from drastic temperature changes. Mulches provide a neat, uniform look to your landscaping. Mulches reduce the speed of water evaporation while keeping an even supply of water on the upper levels of the soil. Prevention of compaction.
Mulches break the fall of water drops, which can cause the soil to compact and inhibit plant growth.
Soil texture improvement. The soil underneath the mulch benefits as well for example, clay soils get improved aeration, and sandy soils retain water better.