This doesn't really fit in well with the other pages. It could be put under McDojos, but that more financial trickery than bullsh!t trickery.
Lets start with the obvious. 'Chi' energy does not exist. It is not something that can be measured scientifically (and yet is purported to have a measurable and therefore scientific effect); and while internal 'feelings' can be attributed to the power of suggestion or a placebo type effect, that effect does not translate well in a combative situation. Especially to the chi-holder's opponent. Even more so if the opponent does not believe in and does not care about chi. There are many many *hilarious* youtube videos about chi based martial arts failing under the *smallest* independent pressure test. Watch them.
This being said (uh oh) the idea behind chi can have uses. I'm going to ignore the eastern medicine 'stuff' for now as I'll freely admit I don't have the experience or knowledge to get into detail, but my understanding is that similarly to martial chi thinking it comes down to using an incorrect descriptive method to pass on information that actually works. I.E. the reasons are wrong (chi), but the effect of using it (acupuncture/acupressure, dietary and routine changes etc.) give the desired result.
I guess it's close to being a children's story - most have a lesson in there that is useful, but the characters are rather fantastical.
Anyhow, back to 'martial chi'.
In a nutshell, it's an idea. A model. A way of thinking that does not require a degree in physiology or sports science to understand.
Instead of having to know exactly how muscles, tendons, and ligaments work and interact with your skeletal structure, and how kinesthetic chains are made and efficiently used, you use an analogy. In this case 'chi' or rivers of 'stuff' flowing through you.
Everyone has seen rivers or streams. Playing in them as a child gives an innate (if basic) understand of fluid mechanics - water can flow around things, can join other streams or be split into many smaller ones. This analogy has become a staple part of eastern physiology (and probably more) for centuries as it requires very little background explanation for it to work.
My best analogy to this is using how science is taught in schools. You start with basic Newtonian physics, conservation of momentum, balance (centre of mass vs footprint), angles of reflection (bouncing things off walls) etc. Things easily seen when playing ball games in the playground and nice simple mental model for how the world works.
You get further through your studies and you're told that this Newtonian stuff isn't quite right, and needs a bit more refinement. Your model needs updating if you want to do better things with it. This repeats a few cycles until you get to the point where you realise all you have are 'wrong' models. They are right enough to work with for some things, but so far there isn't just one model that a) covers everything and b) is accurate enough for everything (anything?) we want to use it for. There's string theory, M-theory, the currently irreconcilable quantum and relativity models (but BOTH in their own fields 'correct'). They are all used but only in the areas for which their models focus on, at least until Grand Unifying Theory is put forward and tested.
A little off track, but hopefully the point has been made. Chi can be a useful mind-trick or reference model when learning how to move. It can definitely be an easier way to think about it that knowing exactly how you should use each muscle group in turn to get your desired effect. But that is all chi is. A mind-trick, or an incorrect model that happens to be helpful in getting *YOU* to move in a specific way for a specific goal. In this instance, providing you are fully aware that thinking of chi is just a thought experiment, an insubstantial idea that is just there to help you, then there isn't a problem.
If however you believe (or are being taught) that you can transfer chi for martial or healing effects then that is DANGEROUS.
Martially, you will get hurt. You cannot use chi to block, or attack, or slow down your perception of time. You will try, you will fail, you WILL get hurt. The only people this will ever work against are those who have learnt alongside you, and believe, and in doing so intentionally or otherwise 'fake' the chi techniques working.
Medically, you will hurt OTHERS. Your actions in telling them you have transferred 'healing energy' or chi to them will discourage them from seeking professional medical advice. Medical advice that will have a proven track record, peer reviewed evidence that it works regardless of whether you believe in it or not. While not chi based, Steve Jobs believed his 'fruitarian' diet would cure his cancer. That did not work as well as he had hoped, and the really sad thing is that the cancer was diagnosed while it was in a medically treatable stage. That cancer would NOT have killed him if he had gotten it treated as advised by medical professionals. From a medical point of view there is no difference in his belief in his diet, and someone's belief in healing chi energy. Neither have any evidence, any repeatable tests or studies.
If they did then they would be included in the definition of 'medicine' (paraphrased quote: what do you call homeopathic 'medicine' that has been proven to work? Answer: medicine.)
If you have a medical or sports background you probably don't need to use the chi model, and can instead use the more observable, pressure tested, peer reviewed human physiological model.
Either way, be aware of what your model was intended for, where it works and what its limitations are.
And if in doubt, ask a scientist. Or an engineer. Or pretty much anyone who has studied or taught at least one STEM subject to a high level.
You still get the occasional crazies in those groups, but are far less common.