Positive reinforcement training is the practice of giving something reinforcing, something the dog likes and wants, to him after each correct response in training. This increases the behavior you are trying to obtain.
Food rewards are the preferred reinforcer of dog trainers who understand the science behind how dogs learn and understand that punitive training (kicks, leash yanks, shock collars, etc), aside from the ethics of using pain and fear as motivators, can actually be extremely destructive in that it creates fearful, nervous dogs and may even increase owners’ and handlers’ risk of being bitten.
Whichever trainer or training school you chose, I would greatly advise you to ensure that they are using positive reinforcement training. Most punitive trainers won’t advertise themselves as such so look out for murky language like “balanced” trainer (meaning they use both positive reinforcement as well as pain and fear as their motivators of choice). Other euphemisms can include; “no nonsense” or “eclectic”. If in doubt, always ask a potential trainer "what happens to the dog if he gets it right and what happens if he gets it wrong".
….and if a trainer ever tells you that “it doesn’t actually hurt him”, I would urge you to ask them the question “then how does it work to change behavior / how does it operate as a motivator?”
Training with positive reinforcement allows the dog to relax and learn, and strengthens the bond between you and the dog.
Do I have to use food to train my dog?
No, however, you must use something to motivate him. We now know that dogs simply don’t carry out behaviours to ‘please us’ or because they should ‘respect us’. This is simply not how animals operate.
Think about it like this; imagine an animal on a harsh African Savanna. This animal has X amount of energy per day and he has to ‘spend’ that energy wisely. He might spend it finding water, stalking, chasing and risking injury or death in the search for food, looking after offspring or finding and ‘wooing’ a mate, keeping safe from predators and regulating his temperature – to name but a few. An animal who would spend his finite energy on behaviours which don’t help him make a living in the world is not going to last very long. Therefore, no animal is programmed to expend energy on behaviours which result in no personal gain for themselves nor do they operate with a view to changing the emotional state of another being (i.e. making their owners happy).
This is what's known as 'the economics of behaviour' and that is why we use food. This doesn’t make your dog a mercenary, unfeeling creature! Your dog adores you but this is simply how the animal kingdom operates. Your pampered dog might seem a million miles way away from a harsh African Savanna but his inherited instincts and knack for survival are still alive and well in his genes and they drive his behaviour.
You may elect not to use food to get desired behaviours but you must provide a favourable consequence after the behaviour in order for the behaviour to increase. Professionals like food because it is one of the most powerful motivators in animal training. The reality is that you get more strongly conditioned behaviour if you do not limit yourself to just praise or pets alone. Over time, you can expect "more for your money," that is more behaviours for fewer treats. You will also become skillful at incorporating other rewards into training.
Will I always have to food reward my dog?
Certainly not as frequently as for a newer behaviour, but yes, maintenance of established behaviour with (concealed) intermittent rewards is a must. There is no free lunch in behaviour. Think of it this way: you have to feed your dog anyway. You can give it all to him for free in a bowl or you can reserve part of his daily caloric intake and make him earn it! Remember, the same would apply if you were to elect to use aversive training methods (shock collars, prong collar, leash yanking, pinch removal, kicking) – those too would have to be intermittently used to maintain behaviours but why use the stick when the carrot does the job even better?