However, I personally do not feel it has the training value I once believed it had and rarely do it now, for the reason most often cited. Many times instructors will prescribe dry practice to someone who has a flinch in an effort to get over the recoil anticipation. I've found this works very little. Once a student KNOWS the gun will not go bang, they hold rock steady. Once they go back to live fire and the gun starts moving around, the brain switches from dry practice to live fire and the recoil anticipation is back. I've seen it help very few times in the 20 years I've been training. At least for recoil anticipation problems, which is pretty much, most of the shooting problems. Same with ball and dummy. It DEMONSTRATES the problem, but it doesn't help correct the problem.
It is not the right drill for overcoming a flinch. "Ball and dummy" drill is what's needed for that.
I won't expound as there are a dozen threads already on flinching, but through dryfire, you should be training your vision, not just your finger muscles. As you learn to "look the shot off" you will cure that flinch. Once you've learned to really watch the FS through the shot (and learned to call the shot!) you will no longer flinch. It's just not possible to both call your shot and flinch. So if someone's not seeing improvements from dryfire for their flinching, they probably aren't putting their focus/attention where they should. People who aren't told this eventually figure it out, like Grelber did. But in my experience that curve can really be shortened by getting their mental focus away from the trigger and finger and on to the front sight and vision. The ball/dummy drill is just a demo of the problem, not a solution. Solution is in the vision.
2c
https://www.indianagunowners.com/forums/handguns/296037-shooting-problems-any-ideas.html#post4205123
https://www.indianagunowners.com/forums/shooting-sports/62950-unexpected-pitfalls-dryfiring-4.html
https://www.indianagunowners.com/forums/tactics-training/239915-will-dry-fire-help-me-4.html
https://www.indianagunowners.com/forums/handguns/378984-flinching-2.html
-rvb