We are huge advocates of tying a horse in a safe place until it settles down and relaxes. I have seen it take 2 hours and I have seen it take 3 days. But, I have not seen one that does not finally 'give it up' and settle down.
We have a large tree with an over-hanging limb that is about 10 or 12 inches in diameter. We have a 3/4 inch nylon rope with a huge SWIVEL SNAP hanging down from it. The snap is about 5 feet above the ground. A good swivel snap is an absolute 'must'.
I will feed and water a horse in the morning and then tie it out and leave it alone until noon. I do not 'baby-sit' it. I can keep an eye on it from a distance, but I do not want people or other horses close by. I want it to learn to be by itself and to learn that this is not the end of the World. I will offer it water at noon; but most of them will not take a drink. I will leave it there until it stops making circles, stops pawing and fussing around and being nervous and relaxes with a hind leg cocked.
If it never relaxes, I will put it up that evening and tie it back out again the next morning. Repeat until you can tie the horse out and it just stands there patiently like an old dude horse. I do not care if the horse is a 'hot blooded' Arabian or TB or a 2 year old just being started under saddle. I do not even bother trying to train on one until it can be tied and it relaxes. If I get one out and it is looking all over and swinging its butt back and forth, I just tie it up and go get another one to work with.
Sure, you can work one until it eventually settles down, but that can also become a habit and an expected way of doing things from the horse's point of view. What I really want is a horse that does not need to be longed or round-penned or 'worked' before it is worked. A trained horse comes out and stands quietly until you do whatever you are going to do with it and then it quietly goes about doing it.
We do this with EVERY horse we raise, buy or used to get in for training. It is advantageous for all of them -- no matter what their occupation is going to be.
First off, a horse that is fussing around, nervous, worried and upset is NOT going to learn and is not going to be responsive or going tp behave for the farrier or for saddling or anything you might want to do or teach it.
A horse is either in a reactive mode or in a responsive mode. If a horse is in a reactive mode you might as well put it up or tie it out because it is only going to learn to resist and argue. It may not even do the things correctly that it has already been taught to do.
For a horse to be in a responsive mode, it must be settled and be concentrating on its handler / rider. It will learn more in 15 minutes than the reactive horse will learn in 2 hours, it won't be all sweaty and 'wrung out' and won't resent everything you did with it.
This type of training is particularly helpful for the 'herd-bound' or 'buddy sour' horse. That kind of horse should always be tied out where it cannot see its herd-mates or buddy.
It is imperative that you tie one in a safe place and NEVER use cross ties. Tie one long enough that it can move around until it decides to stand still. The snap should always be as high as the horse's withers or higher. My second choice would be a solid wall. Never tie to a fence that a horse can put a leg through or to anything that is not strong enough to hold a horse that might set back. Never tie close to anything sharp or rough and never tie to a pole or post that a horse can get wound up around.