Why is it important to have a universal way to describe your horses height?

It is important to have one set measurement to avoid confusion when dealing with horses and people from Another Country than your own as they likely will have their own method for measuring a horse. An example is the USA using Standard measure versus Europe using the metric system. A 15 hand horse in the US would still be a 15 hand horse in Europe, the only real difference is that in the US hands are measured in inches (4 inches per hand), whereas in Europe they are measured in centimeters ( 10.2 cm per hand).