I see where you were going now. My bad.
I misunderstood you.
Again, I don't wish to be promoting a type of training that the Yangs don't use. If this is something that they frown on, don't do it.
This is only one in a long line of fa-jing training applications that I learned from the Wu family disciple who is my Sifu. It's my particular favorite, it's relatively easy, it's cheap, it takes no special training beyond the form training and basic breath co-ordination, it's fun, it gives people a sense of where they are in their martial application of the forms they've learned, that's why I mentioned it.
I sometimes forget that not all styles of TCC teach these things in the same way.
If you want nicely blueprinted, physics and biology compatible reasonings behind why this works, I simply can't help you. I'm an electronics geek, not a physics major or engineer.
It works if I follow the principals I was trained to use in TCC motion, that's all I know.
I've heard all kinds of things about jing and chi putting out the flame, and it may be. I feel it's the air pressure caused by my appendage traveling through the air, delivering power precisely to one small point in space and then stopping, the air pressure keeps moving, the "power" transmits to the candle flame, the flame goes out. If that's "jing" or "chi", then there you go.
Why would I train this? To be able to determine if I can precisely deliver power at a very small point in space using the movments of TCC as I have been trained. It's a way to test your skill, I guess you could say, without having to punch a real person.
After all, if you can hit that exact spot you need to hit in to extinguish those candles, time and time again, especially when you work your way up to putting out an entire ring of candles in a circle around you as you step and turn and issue in different places, at differnt heights and with different methods of delivery...
You can pretty much deliver that precisely controlled powered against your opponent wherever he may be.
And... it's fun.
Again, I haven't trained with this particular excersize in a long time, and my skill level didn't deteriorate very much at all. I've ALWAYS had trouble putting out that flame with one finger. It's never been easy for me. That I would have to retrain to reach that level again after that amount of time off doesn't surprise me one bit. I would have been more surprised if I hadn't had to do so.
So the skills your are using to do this can just as easily be trained in other ways. Less showy, less jing depleting to the practicioner, but certainly no less effecient.
It's not "necessary" it's not "vital" it's probably not even important to TCC training overall in any way.
But, when all is said and sifted, it is a fun exercise.
That's the bottom line for me.
If I'm not having fun, what's the point?