Adding oil to gas was a valid technique to help preserve old high mileage car engines. I would imagine it may have come into vogue after the elimination of lead from the gas, which was a superlative lubricant, ironically despite its poisonous attributes. If you want to argue that the oil can help preserve today's engine from the ethanol and such, we would probably need years of testing and comparison. Then there is the possibility of long-term risks from doing such. Everything downstream will in fact get dirtier faster - valves, pistons, exhaust, etc. Thus I would not do this on a modern engine, but that is just one opinion.