All fats and oils oxidize. Most comercial products add some antioxidant to limit this. Low temperature also greatly decreases oxidation. While oxidized fats won't make you sick, they taste off (soapy, cartony, etc)

Yes because it will spoil if you don't.

Refrigeration of oils helps restrict the growth of aspergillus mold, which is everywhere, and produces aflatoxin that is bad for the liver.

Mix it once and put in the fridge. Keeps solid and smooth. I do this with the Kirkland natural and it's 100% worth it.