We have better engines now and they provide a lot of power even on 10%.
But back in the day, going 10, 20, 25, 30, 40, and even 50% got tangible results. In our area 40% was the standard fuel for Fast, Slow, FAI and 1/2A. We got it direct out the side door of Logghe Brothers Stamping Plant. Mr. Logghe was bored with the little sheet metal parts that earned his living. He liked high performance engines.
If he blew up an OPS 65 to win a boat race, he still won the race. The guy who saved his engine lost the race.