Dude, just spar with some decent opponents. That way when you get cracked, you'll actually learn something.
If you overheard a coach discussing this practice, you likely misunderstood (assuming he isn't a complete incompetent ****). What is considered pragmatic by old-time coaches is the practice of repetitively tapping yourself on the nose or bouncing a weighted ball off it, to strengthen the cartilage (through breaking and re-breaking, and subsequently healing) - and that's only for people who are naturally inclined to have their noses shatter and bleed out everywhere from the first jab that hits them flush.
The fact most fighters lose in your gym should tell you more about the the effectiveness of this technic.
Not sure how serious this post is, but why hit yourself in the face when you can spar? Your head is not a boxing bag. You keep hitting yourself and you'll probably weaken your ability to take a punch instead of gaining some magical punch resistance. I would also be questioning somebodies sanity if I happened to walk into the gym and he was throwing shots at his own head. Stick to the traditional methods of sparring.
