Many owners clip their dog's long hair coat in the belief that this will keep their dog cool during the hot summer days. Unfortunately, this is not the case. A hair coat actually acts as insulation for a pet, keeping the cold out in winter and the heat out in summer. Clipping is not a good idea in dogs that are not routinely clipped. The lack of insulation only makes them hotter. Since the only way they can dissipate heat is by panting, they have to pant that much harder to get rid of the extra body heat.
A hair coat may need to be clipped for therapeutic reasons such as an underlying skin problem or excessive matting of the hair.