The “regular” and “premium” label at the pump is misleading. The premium gas isn’t better. It’s just different. Unless your car specifically requires higher octane fuel, there is no benefit to paying for it. https://www.kbb.com/car-advice/gasoline-guide/
You get slightly better mpg on premium, just not enough to justify the cost.
Not unless you’re adjusting timing. Premium gas has lower energy per unit mass and per unit volume than standard gas.
> Not unless you’re adjusting timing.
Which, every modern ECU will do automatically based on output from the knock sensors.