Happened to have PBS on the other night, and the late, great Victor Borge was on talking about the history of the piano... In particular, how it was a horribly boring and monotonous instrument until somebody came-along and invented the cracks (between the keys).
That reminds me of an aspect of the equine hoof. Specifically, the frog. There are so many theories and myths about the frog. How it acts as an extra heart. (Nonsense, directly anyway. It hasn't got a lot of blood capacity.) How it must bear weight for healthy hoof function. (Tell that to the countless 'desert-footed' horses who go rock-solid decades without frog loading from beneath.) Etc., etc...
One question folks don't seem to ask is why does the hoof have a frog in the first place? Why didn't Nature just make the whole hoof a continuous case of hard material like the wall? Why make part of the hoof out of relatively soft and vulnerable material?
The answer I see is that the hoof didn't so much need the frog, as it needed the hole the frog covers. That 'missing' pie slice out of the hoof is like the cracks in the piano keyboard. If the hoof wall was an unbroken circle, it could scarcely flex at all. It would have to either withstand all the stresses in full sharpness of impact, or suffer structural failure. In fact, I have too often observed that, when the rear of the hoof is immobilized through improper shoeing, the wall tends to crack right down the toe.
Something's gotta give, so Nature installed a flex-joint by taking-out that wedge of horn at the back of the foot. But she couldn't leave the 'guts' of the foot wide-open, so she put on that leathery cover... The frog. While she was at it, she made the skeleton in the posterior of the hoof out of cartilage, to allow that flex-joint to be used to good effect.
Of course, just because design allowance has been made for flexing under stress, that doesn't mean more flexing is always better. The springs on a car are supposed to cushion the ride, but you don't want every bump in the road to cause the vehicle to bounce like a pogo stick. And, while bridges are designed to yield a bit to the wind, sometimes the concept can go a little too far.
The notion that having the frog on the ground in necessary for 'expansion' and proper hoof function doesn't really hold water either. Heavy draft horses almost always have big, loading frogs. But many of the soundest light horses have fast exfoliating horny frogs that never load against firm ground. Trimming such a horse's heels down to the bulbs to try and get the frog on the ground will only create a broken-back axis and ultimately lameness.
The frog can be recruited to bear considerable load when needed. In fact, when we get hooves that have OVER-expanded (which is to say collapsed and pancaked-out), pushing the middle of the foot back up via frog pressure from a heartbar shoe is an effective way to intentionally contract the foot back into shape. Precisely the opposite of the "frog pressure creates expansion" assertion.