Tar was valuable because it protected essential materials such as ships, rope, fences, roofs, tools, and buildings. In wooden societies, preservation was economically important.
Tar seems humble now because modern materials hide many of the problems it once solved. Earlier economies depended on wood, hemp, flax, leather, canvas, and natural fibre rope. Those materials were useful but vulnerable. If they rotted, leaked, or wore out too quickly, people lost money, labour, cargo, shelter, and sometimes safety.
Tar was especially valuable where water was constant. Shipyards, fishing communities, river transport, farms, and military fleets all had reasons to buy or make it. A good barrel of pine tar represented forest labour, fuel, skill, transport, and a material that could extend the working life of expensive objects.
Tar also fitted into export economies. Northern forest regions could turn trees and roots into tar, pitch, charcoal, potash, rosin, turpentine, timber, and other products. These materials travelled far beyond the forest. A navy or merchant fleet could not rely only on romance; it needed supplies by the barrel.
The value of tar came from usefulness plus scarcity of substitutes. Before cheap petroleum products, synthetic polymers, and modern coatings, a sticky dark preservative could be a strategic material.