If the defect (hole) in the part is small enough or the path length for the leak is long enough, it will be almost impossible for the fluids to flow through the hole (leak). The fluid properties that affect flow are pressure, temperature, and viscosity.
Though the answer seems to be correct, but when taken from that perspective, one will not keep focused on the real reason. The main reason why we shoe horses is for work, which then determines the style and the type of shoeing for the individual working horse. Various types of historical horseshoes.
The importance of the horse in the colonial and Native American cultures is of utmost importance. Native Americans did not have the wheel until Europeans arrived. I doubt there is any way to overestimate the importance of the Columbian Exchange in terms of an expansion of biological diversity. On the other hand, as Akannan points out, the exchange of ideas and ideals is equally important.