Board breaking is just a training tool used by many schools, as does mine, but we don't board break a lot. Training is done with pads and will the plastic re-usable boards. Real wood is only used for testing purposes but to be honest, if you can break the plastic you can break the wood as the plastic boards you have to be in the middle where as boards can be forgiving. However with boards I've come across many with knots in them that make it much more difficult and with our wood, some wood is very difficult especially when doubled up.
With board breaking you have to use proper technique and you must commit fully. Boards are not that big so you also have to be precise. I recall many years ago when my break was the back roundhouse and my Instructor stood right beside me and said I'd better not kick him. This made me more aware of my technique as previously I was swinging my foot and using momentum in instead of shooting it straight back and using my hips to torque my leg to make the break. I have personally found that board breaking has fine tuned many techniques I used including remember to pull the toes back when doing such kicks as snap front kicks and other kicks. Knowing is one thing but performing a kick on a board and not remembering is something you'll only do once if you injure your toes badly. Yes these techniques can be learned by other means however when using techniques like this sparring or in training I've found that both pads and the human body can be more forgiving when making a less then perfect technique ... boards you don't have that luxury.
If I was told that we would never do board breaks again I wouldn't complain however I do see the usefulness of this training tool. And under a qualified Instructor with proper training and time, I see no problems in injuries. Those people you see all gnarled up due to breaking ... this is because they were foolish and thought they could "condition" themselves by hitting inanimate objects repeatedly like seen in movies which is bunk. Those old training ways were stupid then and are stupid now and if you train that way then you got what you deserve.
"IF I COME ... I'M BRINGING THE PAIN WITH ME"