In earlier centuries, people used body parts to make measurements. They might take 50 steps and call the distance 50 feet or measure the height of a horse in hand spans. What were the advantages and disadvantages of these types of measurements?

Well, I guess the advantage is that you don't have to find a measuring stick. However, the disadvantage is that not everybody has the same stride length and the same hand length. Of course a 6 foot person would have longer strides than a 4 foot person.