Wood tar can be relatively eco-friendly in some traditional uses, especially when made from responsibly sourced wood and used to extend the life of timber, but it is not automatically harmless.
Wood tar has an obvious environmental appeal because it comes from trees rather than fossil coal or petroleum. It also fits repairable outdoor work: a gate, boat part, fence, or tool handle can be maintained instead of thrown away. In that sense, wood tar can belong to a durable material culture.
But eco-friendly is a broad claim. Tar-making produces smoke and by-products. Wood has to be harvested, transported, and heated. The tar itself contains complex smoky compounds and should not be treated as something to pour into soil or water. Natural origin does not mean environmental innocence.
The strongest case for wood tar is appropriate use. A modest amount used outdoors on timber that would otherwise rot quickly may be defensible. A careless application in the wrong place, or disposal into drains and ground, is not. Product additives also matter because modern tins may not be pure traditional tar.
A careful answer is that wood tar can be a lower-impact traditional option in the right setting. It should still be handled as a potent preservative material rather than as a harmless natural decoration.