Mats are extremely uncomfortable for your pet, and something that should be avoided.
When matted, it can be hard for the coat to fully dry out, trapping moisture close to the skin which can lead to bacterial infections and painful skin damage.
When there is matting around the private areas, and there is nowhere for the poo to go, it becomes trapped close to the skin and can cause a severe infection.
Sometimes, with extreme matting, the affected areas can become so infected that surgery is needed to remove the dead and damaged skin cells.
Matting can also hide parasites like fleas and other skin problems.
Brush your dog's coat regularly, or have your groomer brush it if you don't have the time.