but that comes at the cost of performance, and you still run an elevated risk of engine knocking. For those engines that require it (as stated by the manufacturer) it's the only way to obtain the engine's stated performance, and it also helps with longevity.

Anecdotally, it seems like a more common requirement for turboed engines; for a long time that could be avoided by just buying domestic, but now even some of those engines are requiring mid-grade or premium (if memory serves, the RAM TRX required 91, and I know that GM's 6.2 V8 (which is not turboed) also requires 91).