Lets say you have a car full of 200 lbs adults. You are about to go uphill and you want to pass a slow moving vehicle. You press on the accelerator hard, if you are not using premium gas, your engine will sense detonation and will retart the timing automatically, thus, reducing the power to the engine. Basically, anything you put a heavy load on the engine and if you don't have premium gas, there's a pretty good chance that the car will retart the timing to minimize detonation.