Like anything else you can take it to extrems.. In my own experience you don't have to go to those extremes to see the benefits. But some people do, just to see how far they can take it. Like lifting weights. Most people get good results and have good benefits from it., then there are guys like this. Is it worth it? They think so. If you don't like it, don't do it. Lots of people think martial arts in general is stupid. Spending thousands of dollars and a life time of training for a theoretical fight you will never have.
Best not to judge others.
Is hardening your knuckles/fist worth it? Sure. Is doing it to the point you disfigure it, and more than likely give yourself arthritis (which will also prevent you from making a proper fist, and mess with your grappling/locks)? Not in this day and age.