Update: I looked around a bit and found more information on the subject. Some excerpts-
"cientist Luca Bein at the University of Zurich in 1983 brought to light interesting findings about shock absorption in the hoof, comparing it in unshod and shod (with various materials) hooves. According to his study, a hoof shod with a normal metal shoe lacks 60-80% of it natural shock absorption.
He also found that "A shod foot moving on asphalt at a walk receives three times the impact force as an unshod foot moving on on asphalt at a trot."
An in vitro model was developed and validated in vivo to quantify the attenuation (dampening) of impact vibrations, transmitted through the lower equine forelimb and to assess the effects of horseshoeing on this attenuation. The transsected forelimbs of 13 horses were equipped with custom-made hollow bone screws in the 4 distal bones, on each of which a tri-axial accelerometer could be mounted. The limbs were then preloaded while the impact was simulated by dropping a weight on the steel plate on which the hoof was resting. At the hoof wall, the distal, middle and proximal phalanx and at the metacarpal bone, the shock waves resulting from this impact were quantified. To assess the damping effects of shoeing, measurements were performed with unshod hooves, hooves shod with a normal flat shoe and hooves shod with an equisoft pad and a silicone packing between hoof and pad. The in vitro model was validated by performing in vivo measurements using one horse, and subjecting the limb of this horse to the same in vitro measurements after death. Approximately 67% of the damping of impact vibrations took place at the interface between the hoof wall and the distal phalanx. The attenuation of impact vibrations at the distal and proximal interphalangeal joints was considerably less (both 6%), while at the metacarpophalangeal joint 9% of the amplitude of that at the hoof wall was absorbed, leaving approximately 13% of the initial amplitude at the hoof wall detectable at the metacarpus. Compared to unshod hooves the amplitude at the hoof wall is 15% higher in shod hooves. No differences could be observed between shoe types. At the level of the first phalanx and metacarpus the difference between shod and unshod vanished; it was therefore concluded that, although shoeing might influence the amplitude of impact vibrations at the hoof wall, the effect of shoeing on the amplitude at the level of the metacarpophalangeal joint is minimal."
"That metal shoes increase concussion / vibration is not in question, it is long proven and accepted - this is a main reason for the development of all manner of pads and even rubber shoes in an attempt to prevent increased concussion - indeed pads have been show to offer less concussion, but do not negate the other negative effects on the hoof"
Etc etc. Found at Healthy Hoof - Solutions for Barefoot Performance
I don't mean to sound one sided if I do, I think there are multiple situations where shoes would be the smarter choice. I just don't see why it is assumed that horses need shoes. A horse should be evaluated first before shoes are deemed necessary, there is no need to put shoes on a horse unless it has benefits.