As the owner of two full grown boxers, Zoe & Hayden, I can tell you a conditioned animal is better off -- happier, more alert, more content. The animal will sleep better, have more energy, and be better adjusted. Exercise will also benefit your dog by keeping him lean and trim. Physically active animals have stronger and healthier bones, stronger cardiovascular systems, better muscle tone, and fewer everyday problems.
One of the biggest problems with pet dogs is that the only activity their owners share with them is feeding, and this becomes a reward system. It becomes a form of positive feedback for the owner and the pet and the animal gets fed too much and gets fat.
Exercise should be built into every dog's daily routine, but if you plan to take it walking, jogging, or camping, additional physical conditioning is essential to build your animal's stamina. The first step should be an examination by your veterinarian. A half-hour walk in the morning and another half-hour at night should be sufficient for 90% of all dogs.
Those owners who anticipate strenuous exercise for their pet should provide additional levels of conditioning. Begin several weeks in advance and slowly increase your dog's exercise period each day. Start slowly, maintain a regular routine, and never push your pet beyond its capabilities. An adequate goal is a minimum 30-minute exercise session, three times a week. That includes a 5-minute warm up, 20 minutes of aerobic activity, and 5-minute cool down period. My personal form of exercise with the dogs is a brisk walk up in the mountains. Just remember fido needs to work out too.