The octane rating of gasoline is a measurement of the efficiency of the burn. Gasoline is draw into the cylinder, it is push up by the cylinder, where it is ignited, pushing the cylinder down. With multiple cylinders, this is all coordinated via the timeing sequence. Therefore, if you put high octane gasoline in a car were a lower octane is rated, you are not going to get more power or miles per gallon. In fact the efficiency of the car's performance may be harmed because the higher octane gas may ignite to soon, thus putting the strokes of the cylinders out of sync. Using low octane fuel in a car designed for high octane fuel will to the same thing, except, the combustion stroke may fall behind.
Using the wrong octane is what usually results in the knock and ping you hear in a car. The knock is more of a rattling sound. Ping is like something tapping inside the engine. I use to work for the oil and gas industry. I had this discussion with several engineers over the years. Now on my own experience, I will sometimes fill my tank half with regular and half with the higher octane, in order to get the cleaning effect. I only do this once in a while and only if the car is acting sluggish.