Having mulch in your garden beds helps to regulate the temperature of soil and retains ample moisture to create a damp environment for plants to grow. When it’s hot outside, the moisture in the soil begins to evaporate which dries out your garden bed. Rock doesn’t create this atmosphere but mulch does. Mulch keeps your plants insulated which protects them from harsh weather conditions. For a detailed analysis on this question, read my blog 3 Reasons to Remove Rock and Install Mulch. To alleviate any suspense, I end up concluding that mulch is vastly superior to rock.