Winter in our area is unpredictable to say the least. Yet, your trees, shrubs and perennials have to stand out there and take whatever Mother Nature heaps upon them. You will have healthier, happier plants if you put boots on them.
Boots? Yes, to protect their feet (roots). We know plant boots better as mulch. Organic mulch moderates the soil temperature, reducing the effects of extreme cold or unseasonable warmth. It also absorbs some of the water from winter rains and melting snow so as not to drown the plants. It then releases the water in a more controlled manner for the plant to use over time.
Spread up to four inches of organic mulch around the base of your plants. However, do not let the mulch touch tree trunks and shrub stems. In particular, do not pile the mulch up the trunk in a mulch volcano.
I recommend organic mulches like wood chips and pine bark because they do double duty. While the mulch insulates the soil during the cold weather, it also decomposes and returns nutrients to the soil. I am particularly partial to double ground hardwood mulch because it is made from recycled debris from tree trimming operations. Recycling this material contributes to plant health while reducing the stream of waste going to landfills. Inorganic mulches like various types of stone chips don’t provide these added benefits like organic mulch.
While mulching to four inches is recommended for winter, it is not for the growing season, so some mulch may have to be removed in the spring. During the growing season, the mulch layer should only be two or three inches thick.
Keeping Our World Green 
We have a neighbor who owns an industrial use chipper for his lawn care business. All of our mulch these days is from this source, as it not only is a cost effective source (free), it also reduces hie waste to the landfill and decomposes as you described to enrich the soil. Buying the processed mulch seems such a waste of money when this raw product does the exact same thing.
You are lucky to have a neighbor with a chipper and a supply of wood chips. Most people don’t have this luxury, so they depend on tree companies like us. Our mulch is also waste from our tree care operations, which we double grind to make it more attractive. We then age it for at least a year, which gives it its dark color. Speaking of color, if the chips you use are tan (indicating that they are fresh) rather than gray or black (indicating that they are aged), you should only spread them on the top of your planting beds. If you work fresh chips into the soil, they can draw nitrogen from the soil. They do not, however, if just spread over the top of the soil.