[digitallis42]

If your engine does not require the higher octane, then no efficiency will be noticed and you're just burning money. If your engine is specified to take the higher octane, then you can notice an efficiency bump over running a lower octane fuel in most modern engines. The engine computer will adjust the valve timing to prevent predetonation with the lower octane fuel at the cost of efficiency.

Adding octane to fuel isn't adding a booster. It's adding stability to the fuel so it can be run in a higher compression engine. If your engine doesn't reach that pressure then you'll notice no effect except your wallet getting lighter.