Its a very important fact to remember that human hands are not designed for hitting things. They are designed for picking up harder/pointier objects and hitting with those instead.
When confronted with the fact that punching a very solid head with our not so solid fists hurts alot, there's a number of ways we can choose to deal with it.
The one which hand conditioning espouses is to make our fists a distinctly more solid object.
Its important to remember however that many of these practices from times when variously there was a shorter life expectancy, and/or a slightly less detailed knowledge of how our bodies function.
This means that the longer term effects of such practices may not have been explored or documented too thoroughly. Especially given that most information regarding the practices is anectdotal, and that there's been no proper detailed surveys and investigations that I know of.
If anyone has a link to one I'd quite like to read it?
But there is a fair chance that such practices can mangle the hand, and till more info is available, I'd be wary of going that route.
Another solution and the one I endorse ( so you know its good)

is that of not trying to hit really hard objects with your fist. Use the less breakable parts instead, like hitting with the heel of your palm instead.
Or more enjoyably hit them with your elbows and knees instead.
Save your fist for hitting the soft parts, and working the body instead.
And third of course the historical favourite of hitting them with a rock instead. Low-tech yes, but it retains that nostalgiac charm of a time when men were men, women only slightly less hairy than men, and nature was something that tried to eat you.