I use polyunsaturated oils to attempt to preserve the wood used for my raised garden beds. While vegetable-oil preserved wood might not be as long-lasting as a modern chemical stain, modern stains have various amounts of heavy metal, which I don't care to put in close proximity to plants I intend to eat. The catalogue has a paint sold for raised beds, but discarded vegetable oil is free.

Paints and stains were traditionally made with linseed oil/soybean oil (and other similar thin oils) because these combine spontaneously with oxygen in the air to form a hard film. Modern stains are made with petroleum distillates.

Dietary polyunsaturated oils facilitate the creation of lipofuscin [0], the age pigment. Dietary polyunsaturated fatty acids also drive lipid peroxidation [1] chain reaction, whereby unstable unsaturated oils combine spontaneously with oxygen in the body to break down in an uncontrolled manner. The end products of lipid peroxidation wreck havoc by combining with proteins to make "fluorescent polymerized compounds" [3], etc. Eating polyunsaturated fat won't make you fluoresce, it'll just make you old prematurely.

The Omega-6 polyunsaturates are especially good for facilitating inflammation, due to their use to create Prostaglandins [2].

I do not consider polyunsatured oils edible, and read labels to avoid them.

[0] https://en.wikipedia.org/wiki/Lipofuscin#Formation_and_turno...

[1] https://en.wikipedia.org/wiki/Lipid_peroxidation

[2] https://en.wikipedia.org/wiki/Prostaglandin

[3] https://europepmc.org/article/med/7001991