If you're wondering why this feels good its because being hit in the balls isn't just about pain, it makes you sensitive to everything. You can get used to this discomfort and then you're mostly just left with the increased sensation where you can cum from it. A hard smack in the balls right before an orgasm will make you ejaculate harder.
I have been wacking it for over 50 years. I have seems thousands of guys wacking it both in person and one the net. Not once have I ever seen that method used to achieve that goal. That said it would appear to have been very successful. I guess I am going to have to go out and buy a tiny hammer to beat my tiny tool.