How useful is Bruce Lee's 1-3 inch punch

Bruce Lee did several demonstrations and among his most famous was the 1-3 inch punch....
Holding a fist 1-3 inches away from it's intended target it, the punch would be fired shortly following a short twitch by the puncher, and back/down goes the assailant.
Bruce is seen sending men his size into a chair behind them after this small movement. As impressive as it looks, I just ponder the effectiveness and usefulness of such a weapon.

Dan Inosanto (Bruce Lee's successor) demonstrated that the purpose of it was for trapping, and close range fighting.
The movement you need to learn to get it, opens up other things as well.

I Just used it today with a student, measured his ability with it initially, then returned to it after some related exercises and was astounded at the results!
It's practical but when used at the right time.

What are your thoughts?