Octane Overdose
"If some is good, more is better" thinking does not apply to octane. Here the rule is to supply whatever octane the engine is rated for and call it done. Higher-than-required octane does not yield more power or mileage, only oil company profits.
Some engines are rated for premium 91 octane fuel but can burn 87 octane regular, thanks to the magic of knock sensors. In that case, run regular gas if puttering around surface streets, and premium fuel if full-throttle driving is part of your daily repertoire.