There is no particular reason to bathe your dog, unless he or she has ended up covered in dirt or mud.  However some dogs with oilier coats do tend to have more of an odour than others and you might prefer to be with your dog if she or she smells fresher.  Bathing can improve the appearance of a dogs’ coats by removing dead hair but keep in mind that frequent bathing can rob your dog’s coat of its natural sheen and make it harsh and dry.  For most dogs, regular brushing will keep the coat and skin in good condition, eliminating the need for frequent baths.
If your dog has special coat needs you may wish to consult a breeder or professional groomer for recommendations.
Most vets recommend dog shampoo no more than once a week if you want to lather up your pooch, although plain water from a hose on a warm day might be enough.  In cooler weather, baths should be indoors in a tub or basin, in lukewarm water.  Some recommend plugging the dog’s ears with cotton to keep water out of ear canals which are predisposed to infection.
A nice blow-dry to finish off is the quickest way to dry your dog, as long as the noise doesn’t bother them too much.  Otherwise a good rub with a towel will do the trick.
For some dogs, bathing comes with a good scrub and massage which they love – check out this spa session!  Spa Day!