A choke chain is the best training tool. It will not harm the dog in any way when used properly.
There is a huge difference between a correction collar, also known as a choke chain and a just a collar. There are some people who consider that a choke chain is rather inhumane. This is because they have not used it correctly or have not been shown how to use it. A correction collar chain works on a jerk and release motion and distributes pressure equally around the neck region. A quick motion to train a dog. On the other hand a flat web or leather collar concentrates pressure only on one part of the neck on the side opposite the leash.
 
So if a flat collar is jerked from above, the entire pressure is focused on the windpipe, which causes a strangulating sensation for the dog. Thus the choke chain is a better alternative.

 

A Correction Collar (Choke chain) should never be left on the dog when unattended.
A Correction Collar is for training, walking and is used in the show ring.
 

A correct fit is an absolute must.  

The chain should have at least 2 or 3 inches of slack when it is pulled snug around the dog’s neck. Please note that a short chain will fit rather too tightly and a long one will make it difficult to deliver the quick snap that is required for an effective choke chain correction. Do not use thin linked jewelry type of choke chains other than for the show ring, they are not strong enough will they can bend or break. Remove your dog’s regular flat collar when you use a choke chain. The flat collar might dissipate the quick snap of the choke chain making it an ineffective training tool. Material "choke" collars can be hard to find but  are great for pups.

 

Use of the correction collar, (choke chain)

Hold the chain out horizontally, and then drop a loop through one of the end rings forming a big letter ‘P’. With your giant at your left side, Put the chain over his head so that the long portion of the chain, which is the straight part of the ‘P’, hangs down his neck. When you want to train your dog on the right side, just reverse the chain. The weight of the chain length pulls the chain down forming the p when relaxed.

 

 What requires some amount of practice is learning how to use it effectively.

When you use it your dog must get the clear message of what is correct. The secret is to apply pressure and release immediately. It might take a little practice to get the correct and quick snap and release action of the choke chain. Make it sharp and quick. It is a matter of training. Placing the chain above the muscle band just behind the giants ear. People normally tend to apply pressure on the chain and hold it. This causes the dog’s neck muscles to tighten. So he pulls away from the pressure. He does not surrender to it. So instead of correcting your dog, you just promote resistance in him. The amount of force used is also important when using a choke chain. The fact is either you correct your dog or you do not, no maybe.  So if you jerk and there is not enough force applied your dog will not get the message and he will continue with whatever he was doing. This will defeat your very purpose of using a choke chain. So you must correct as hard as you can and get the message across. You will know that he has got the message when he stops whatever he was doing and looks at you. So praise him when he stops his incorrect behavior and looks towards you. When he stops his wrong behavior and looks at you, he has accepted your leadership. That is good communication and the whole point of correction.