One of the major benefits of having two dogs rather than one is that dogs are pack animals that are hard-wired to live in social groups. A dog that is left alone for long periods of time can become nervous, timid or even overly aggressive. In households where humans are gone for significant portions of the day, having more than one dog is a kind and sensible thing to do.
Separation anxiety that occurs in dogs that are left alone can result in significant destructive behaviors. Incessant barking, for instance, may be viewed as a neighborhood nuisance and is often the direct result of anxiety that a dog feels in response to being left alone. Dogs left home alone also might chew on household objects and furniture as well as get into the trash and spread it all over the house.
Other benefits of having two dogs include the added security factor. Even small dogs often dissuade potential thieves and other prospective household intruders by barking, so two dogs barking at once is an even greater deterrent. Dogs are also good for sounding the alarm in the event of fire or other imminent threats, and many people like the added companionship that they gain from having more than one dog in their household.
The decision to include another dog in the home is not one that should be made lightly, however. A great deal of thought needs to be given to issues such as increased food costs and whether additional veterinary bills are likely to be too big of a burden. An alternative to bringing another dog into the home is to arrange for doggy day care services for those times when the family dog would otherwise be left alone for a long period of time.