I'll do my best to explain. Metal therapy was something that was used way back in the day. It is really hard to find much info on it. Most of what I have learned is through trying it out and talking to others.
The most noticeable effect is the release of that excess energy. It changes depending on what I am wearing and where.
When I was doing my research I actually ending up looking at conductivity vs. Resitivity. Metals, crystals, and the human body all conduct energy in different forms. From what I have found it is why we pair well with crystals. However metals are actually more conductive which is why we also pair well with them. It has to do with temperature. The hotter anything gets the harder it is for energy to pass through. I believe that is why salt baths work well. Slat is a metal and it is very conductive. Size also matters. When energy passes through an object it brings up the temperature. When a object gets hot it can still absorb energy but the energy will not pass through it. It's why Crystal's need to be cleaned and break if they are not. Imagine a balloon that gets continuously filled, it'll burst. Metals can handle more energy than crystals and the human body. It takes much longer for them to get so hot that the energy gets stored rather than released.
With that in mind I started to think about where I had noticable energy blocks, and also where I had energy leaking out. It seemed that the places coincided with one another.
So that necklace I had kept breaking because a lot of my energy was getting stuck in my neck between my shoulders. I felt great wearing the necklace because it was allowing the energy that was stuck in that area to be released, but it was too much for the necklace(it is a lapis lazuli necklace btw).
I noticed that from my hands up to my wrist there was also a lot going on energy wise. My right soaks up energy and my left releases it. When I first put the three metal bracelet(copper, nickel, and brass) on I felt the best I had ever felt. So I bought rings and extra bracelets and then I came across some interesting issues. The effects where not the same and I couldn't figure out why.
However through talking to people and some trial and error I began to think of the human body like a circuit board. If the connections are not in the correct place the energy cannot flow properly.
That got me to thinking about my necklace and how having multiple bracelets was not working. One of the energy workers I spoke to said it was because I was grounding too much. Essentially I was draining all the old energy which was good. However I was draining out all my energy without replacing it.
So I stopped wearing all the bracelets all the time. I bought a copper necklace, a silver necklace and some silver studs. I alternate between those only really tough days. The silver is really good for emotionally charged days. The copper is great for bodily pain and fatigue. Most days I pair the bracelet on my right wrist with the lapis necklace which I have since added a cerussite stone to. The cerussite is what brings in new energy after the lapis and three metal bracelet ground out the energy and I feel great.(cerussite contains lead, so I recommend finding something that does not. Right now it works grest but I am currently looking for something safer) I am in SF almost every day and while the energy gets to me a little it is nothing like it used to be. If fact the energy that I pick up is manageable. I am also able to understand it a lot better.
My very long point is that it is important to figure out how the energy in your body is flowing. Then you can manipulate it with metals and crystals. Less can me more. I am told gold is great. But it has to be as close to pure as possible. Same with the other metals. Like anything when you add other stuff to something you change it's vibration, or energy signature and thus change its effect. I'm told 22k is fine. But it is expensive. Brass and gold appear to have similar effects and brass is much cheaper. They are supposed to be good for healing the soul energy. Honestly haven't tried it yet.
Also when I have bodily pain I have copper disks that apply directly to that area and after a couple of hours the pain is gone. After a couple of days it doesn't come back. Applying metal disks to injured areas is actually one way metal therapy was used way back when.
I have also learned that when doing energy work it is better to take off the metals. It is much easier to feel what is going on. Although I do think that as I progress that will change.
Hope this was helpful.