Oils are of two types basically..derived from saturated fats n from unsaturated fats..saturated fat oils are those extracted from fleshy seeds like groundnut, coconut , sesame seeds-gingelly oil n milk-ghee n butter ....unsaturated oils r derived from less fatty seeds like sunflower oil, rice bran n flax n olive oil...of the two unsaturated oils r claimed to be healthy..
Since unsaturated oils dont block blood vessels, light to digest n dont get deposited in organs..but leave a lot of carbon when used once..
While saturated oils like gingelly oil , coconut oil etc csn be reused atleast twice..sundrop oil etc should be used only once for frying..the carbon residues it leaves are sure to cancer changes on the long run in cells..
Barbeques though tasty should be restricted for atleast once a month not more than that...
For same reason of generation of carbon residues..