Some good answers, though i'd have to say that "cruel" is possibly a bit harsh, and very much dependent on the actual dog, and the circumstances itself........some dogs really love company to the extent of being impossible without it, therefore finding ways to pass the time, such as chewing, raiding the worksurfaces or consuming the occasional entire tub of butter. However, if your dog is used to spending time alone, and often these are rescue dogs, then it can be ok, and this can be made better by the addition of a second dog. However, in most cases, and definately the case of puppies, it would not be in the best interests of the dog to be left alone for long periods.......