Effects of Neglect: Neglecting the coat of your long-haired dog can cause painful matting. If the dog is shaved to remove the mats, it might feel itchy and scratch its skin raw. Wrinkly dogs like boxers and Shar-Peis can develop dermatitis if their skin folds are not cleaned regularly.
Benefits to Your Dog Brushing: your dog distributes natural oils in its coat that keep the skin healthy. Regular attention to the coat will remove burrs and tangles and help you spot ticks and fleas. It allows early detection of cuts, lumps or skin conditions that are best treated early.
Benefits to You Brushing your dog regularly establishes trust and physical closeness and controls shedding and dander, which can cause allergies.
Fun Fact: Even hairless breeds require grooming. Their patches of hair need to be combed daily to prevent tangles, and their bare skin needs to be washed, oiled and protected from sunburn.
Source: "The Original Dog Bible"; Kristin Mehus-Roe; 2005