* You absolutely will have fewer weeds
* Watch your water bill drop because your plants and soil are losing less precious water
* Less soil compaction from driving rains and perhaps foot traffic (from two and four-legged family members)
* Insulating soils from extremes in temperature fluctuation. That works both ways to benefit plants. Soil temperatures drop more slowly in the fall under mulched soils. Roots continue to develop while soil temperatures are above 40 degrees F. Durng the heat of summer plant roots benefit from cooler soil temperatures, too
* Mulches provide organic matter that improves soil structure. Mulch also increases microbial activity that converts organic matter into nutrients
* Research indicates pine fines or pine bark mulch actually have innate fungal-inhibiting properties that make them a smart choice to use for rhododendrons and azaleas
May I just get this one pet peeve off my chest? Why do some landscapers insist on building beaver dams of mulch? You've seen what I'm talking about. Unfortunately, it's an all too frequent occurrence. The mulch is mounded around the trunk at least a foot deep. Guys (women would never do this), root systems need oxygen- just like your lungs. Beaver dam mulching not only reduces oxygen to roots, it keeps bark tissue wet. Wet bark is subject to all kinds of issues. When bark tissue isn't healthy, that's stress. Plant stress often leads to insect and disease problems. Enough said?
We know it isn't difficult to mulch properly. Leave a two to four inch diameter opening of naked soil from the trunks of trees, or the outer edge of multi-stemmed shrubs. Spread mulch there, away from stems. In dense clay soils a one to two inch depth is fine. For sandy soils applying a three to four inch layer of mulch is appropriate. Extend the mulch as far as feasible within the context of your garden beds or lawn.
I heard a presentation a few years ago that I thought was interesting. Yes, you would probably be surprised at what I find interesting. Whenever possible, try to replicate what the plant would receive at its feet in nature. So, for trees and shrubs, consider using wood-barked based products that are broken down by fungi. For soft-stemmed annuals, perennials and veggies use "green" mulches that are dominated by bacteria- compost, leaf mulch, cotton burr compost, for example.
Don't get hung up on trying to match different mulches throughout your landscape. The most important thing is to mulch, rather than NOT. Don't forget one last benefit of mulch- appearance, appearance, appearance. In addition to all the documented physical benefits mulch acts as a unifying element. It ties your plants together visually in a way that is very pleasing.
You don't know how lucky you are I didn't get started on white marble chip "mulch".