This technique if I recall correctly from studies comes from Buddhism or Zazen a bit. Young monks were perplexed their master could not be bound by emotions. He explained emotions are only visitors. It got adopted and cleaned up a bit for Western cognitive behavior therapy as, you are not x emotion, you control x emotion. It is highly effective but I wonder at what cost at times. It teaches us to disassociate I think. we can walk away from what we feel, we're not feeling it.
I am already cleared to do something I learned, ought not have, yet did. I find myself shutting off emotionally at times. This for me is a means to cope. It is painful upon returning from the hiatus. I have to force myself to feel anything, anything at all. And in this shutting down, I do not even feel numbness, I feel nothing the unnamed nothing. I exist but only barely at that point.
Over the past year or two, saw a lot of loved family go onward. It got too much. I spoke with a therapist and suggested I shut off. I've been monitored so as to not go off the rails and become a danger to myself or others. I kept one thing as an anchor, the love for my wife and our critters. Even now, it is hard to gradually return to feeling.
The technique you suggest here does work for its intention. I would suggest people seek professional help though. It can if improperly used cause more harm than what good it is intended to be used to achieve. You may become too aloof and not want to return to take care of yourself.
This sounds a lot like the instinctive method I've always used, to not let negative emotions overwhelm me -- what some therapists, and I, call "stuffing" emotions -- just shoving it down, out of sight, out of mind... actually a form of denial, I think. It's how my depression works -- depression allows me to stuff all those things I don't want to feel... the downside is that they haven't actually gone anywhere, they're all still there, and ONE DAY, they will emerge, usually distilled into such a potent mix of rage and pain that I or someone else or some object gets hurt.
This was how I coped, when I was too young to drink; once I started drinking, it facilitated the stuffing, but even after I got sober, the stuffing didn't stop; in AA sometimes it's known as "harboring resentments," and is widely known to be detrimental to sobriety -- just because eventually those stuffed and harbored feelings do emerge, and if we're not ready to cope with them, it *can* lead to a drinking relapse -- I had an instance of the emergence when I was just about 15 yrs sober, and my depression was all mingled with PTSD and peri-menopause -- basically a perfect storm of the worst possible emotions, but fortunately, I didn't drink, I maintained my sobriety because it had become... a habit.

But it took 2 yrs of Effexor and some good therapy to get past it. Now if I feel something, I try to let it out immediately, or as soon as I can, so it doesn't sit inside me and ferment.
Andria