Race trainers use all manner of "grips and grabs" on shoes to to affect how the horse's hoof encounters the track surface -- for soundness as well as performance. The gist of this study, suggests researcher Christy Mahaffey, is that shoeing does not affect performance nearly so much as the track conditions:
"Shoeing had little effect on loading during the primary and secondaryRacing is an extreme sport, but maybe the other disciplines should take notice. We ask a lot of our farriers, and sometimes expect miracles. A great farrier is still a great farrier, and the hoof has to be balanced -- but in the end, the footing horses work on may have the greatest impact on a horse's soundness.
gait phases when the hoof comes in contact with the surface and slides
forward,” Mahaffey said. “What was also really interesting is that
changing the moisture content in the dirt surface did have a significant
effect on the loading—much more so than using different shoes.”
Disclaimer: Nothing in the article suggests that we should extrapolate from racing to dressage, or to hunter/jumper disciplines. I just think it makes sense.