There are many benefits of mulch some of which include moisture retention weed control and landscape appearance, but too much of anything is never a good thing.
Excessive amounts of mulch can harbor problems like disease, pest and create the perfect environment for other challenges like fungal infections around your plants and trees.
A micro thin layer of mulch on the other hand is not enough to block the weeds and control the soils moisture levels.
In most sustainable landscape designs, ornamental landscape beds and perimeter landscaping should receive, 1.5 to 2 inches of mulch. For problematic weed areas, install a 2-3 inch layer of mulch may be necessary.
Many materials available in the bay area for commercial lawn services include fir bark which is very expensive, and fades out over a short period of time. So consider using environmentally friendly recycled materials that have been died with natural colors like mahogany or cedar color and are safe for the environment lasting much longer than conventional fir bark.