Dogs will normally 'blow' their coats twice a year.  In the spring, the winter coat will come out to make room for the cooler coat to come in.  In the fall, again there goes the summer coat to make room for the winter, warmer coat to emerge.  These rules apply to double coated dogs only. (eg. Malamutes, Huskies, Shepards, Goldens, Chows, Aussies, etc)

The rules for the other breeds are, the more comfortable in the house they are the better.  A long coat or matted coat can make a dog that only goes periodically very uncomfortable. 

 Imagine sitting in our home with a fur coat on!! (eg. Shih Tzu, Maltese, Schnauzers, Poodles, etc)