What is the Practical application of law of polygon forces?

There are many practical applications. here's one: On my farm, I often need to uproot trees and stumps. If I hook a chain to my tractor and a tree/stump and try to drive away, the force holding the tree in place overcomes the force holding my tractor tires to the ground, and the tires slip. So I hook the chain to the tree I want to remove, and (tautly) to a larger one nearby instead of to my tractor. I then hook a second chain to the middle of that chain, and the other end of the second chain to the tractor. I then drive the tractor away perpendicularly to the first chain. I am in essence adding (a portion of) the force holding the larger tree in place, to the force being applied to the tree I want to yank free. Put another way, I am creating more pulling force on the stump to be yanked, with the same motive force limit on the tractor (the point at which the tractor slips.) Do NOT try this without experience, because of the risk of chain snapping and taking your fool head off. I haven't bothered to describe my safety procedures ( among other things I tie the chain off at several crucial points so that if it snaps it can't reach me or my equipment) because those procedures aren't pertinent to the question.