> An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without causing engine knocking. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates the resistance to detonating under pressure without a spark.

from https://en.m.wikipedia.org/wiki/Octane_rating

It just lets higher performance cars achieve higher compression ratios. I believe technically this means it has a little bit less raw combustion potential the higher the octane rating. But none of this actually matters in practice as long as you feed your car what it asks for.

It means we can run higher compression in our engines without engine knock, which means we can run our turbos and timing harder on a smaller dispacement engine without ruining it, meaning more efficient engines.

Cleetus McFarland ran a car on brake-clean which has really low octane rating so sure anything works if you care about nothing. https://youtu.be/0hYOgGYQ_c8

American big block naturally aspirated engines will be tuned for crap fuel, if you've got a modern efficient turbo engine you should buy premium fuel to not ruin your engine.