One of the things that irks me all the time is people who think they gain some benefit from using higher-octane gas than their car recommends.
The idea of higher octane is that it retards ignition--meaning it's harder to burn than lower octane.
This is important, as you point out, in very high compression performance engines. In those engines you need to retard ignition because the heat and pressure will cause ignition before the spark goes off if your octane is too low... Which is very very bad. Modern cars can compensate for this such that if you put 87 in a car that recommends 93, it won't be horrible, but it's not good.
If your car DOESN'T have high compression ratios, there is literally no benefit whatsoever to higher octane than your owner's manual recommends. You're throwing money right down the drain.
I liken it to the misplaced idea that people have that bottled beer is better than canned, because premium beer comes [actually should be past tense now that so many craft beers have canning lines] in bottles. But bottles are actually inferior packages to cans in almost every way, yet people will fool themselves to think beer tastes "better" out of a bottle because they associate bottles with premium.
Same with cars. High-end sports cars require higher octane, so people assume it must be better gas. But it's not. It's actually in one way worse [harder to ignite] but that's a benefit in a high-compression engine. It's no benefit otherwise.
